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 $117.46   13.785%   $133.6519   $133.65   $133.65   $133.70  
  Purchase #2 $188.62   11.521%   $210.3509   $210.35   $210.35   $210.40  
  Purchase #3 $181.77   3.455%   $188.0502   $188.05   $188.05   $188.10  
  Purchase #4 $111.37   12.812%   $125.6387   $125.64   $125.65   $125.60  
  Purchase #5 $244.90   13.277%   $277.4154   $277.42   $277.40   $277.40  
  Purchase #6 $40.80   11.133%   $45.3423   $45.34   $45.35   $45.30  
  Purchase #7 $60.52   12.202%   $67.9047   $67.90   $67.90   $67.90  
  7 purchase totals = $945.44       $1,048.3541   $1,048.35   $1,048.35   $1,048.40