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 $34.88   5.234%   $36.7056   $36.71   $36.70   $36.70  
  Purchase #2 $49.86   10.408%   $55.0494   $55.05   $55.05   $55.00  
  Purchase #3 $54.98   7.171%   $58.9226   $58.92   $58.90   $58.90  
  Purchase #4 $152.89   9.593%   $167.5567   $167.56   $167.55   $167.60  
  Purchase #5 $44.49   8.611%   $48.321   $48.32   $48.30   $48.30  
  Purchase #6 $26.79   6.607%   $28.56   $28.56   $28.55   $28.60  
  Purchase #7 $211.97   5.816%   $224.2982   $224.30   $224.30   $224.30  
  7 purchase totals = $575.86       $619.4135   $619.42   $619.35   $619.40