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 $66.49   11.202%   $73.9382   $73.94   $73.95   $73.90  
  Purchase #2 $165.45   7.337%   $177.5891   $177.59   $177.60   $177.60  
  Purchase #3 $30.60   4.788%   $32.0651   $32.07   $32.05   $32.10  
  Purchase #4 $93.73   3.696%   $97.1943   $97.19   $97.20   $97.20  
  Purchase #5 $35.35   8.361%   $38.3056   $38.31   $38.30   $38.30  
  Purchase #6 $243.93   11.632%   $272.3039   $272.30   $272.30   $272.30  
  Purchase #7 $24.72   11.823%   $27.6426   $27.64   $27.65   $27.60  
  7 purchase totals = $660.27       $719.0388   $719.04   $719.05   $719.00