Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $175.92   10.293%   $194.0274   $194.03   $194.05   $194.00  
  Purchase #2 $116.30   6.562%   $123.9316   $123.93   $123.95   $123.90  
  Purchase #3 $193.57   8.776%   $210.5577   $210.56   $210.55   $210.60  
  Purchase #4 $106.91   3.180%   $110.3097   $110.31   $110.30   $110.30  
  Purchase #5 $228.80   8.374%   $247.9597   $247.96   $247.95   $248.00  
  Purchase #6 $157.53   13.309%   $178.4957   $178.50   $178.50   $178.50  
  Purchase #7 $126.73   13.241%   $143.5103   $143.51   $143.50   $143.50  
  7 purchase totals = $1,105.76       $1,208.7921   $1,208.80   $1,208.80   $1,208.80