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 $96.77   4.696%   $101.3143   $101.31   $101.30   $101.30  
  Purchase #2 $201.42   10.538%   $222.6456   $222.65   $222.65   $222.60  
  Purchase #3 $22.95   5.656%   $24.2481   $24.25   $24.25   $24.20  
  Purchase #4 $30.69   3.272%   $31.6942   $31.69   $31.70   $31.70  
  Purchase #5 $178.26   6.104%   $189.141   $189.14   $189.15   $189.10  
  Purchase #6 $217.51   7.538%   $233.9059   $233.91   $233.90   $233.90  
  Purchase #7 $39.56   12.441%   $44.4817   $44.48   $44.50   $44.50  
  7 purchase totals = $787.16       $847.4308   $847.43   $847.45   $847.30