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 $119.42   3.284%   $123.3418   $123.34   $123.35   $123.30  
  Purchase #2 $121.82   12.136%   $136.6041   $136.60   $136.60   $136.60  
  Purchase #3 $240.47   7.176%   $257.7261   $257.73   $257.75   $257.70  
  Purchase #4 $136.39   6.710%   $145.5418   $145.54   $145.55   $145.50  
  Purchase #5 $102.51   4.745%   $107.3741   $107.37   $107.35   $107.40  
  Purchase #6 $188.96   6.642%   $201.5107   $201.51   $201.50   $201.50  
  Purchase #7 $51.55   5.686%   $54.4811   $54.48   $54.50   $54.50  
  7 purchase totals = $961.12       $1,026.5797   $1,026.57   $1,026.60   $1,026.50