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 $148.45   9.104%   $161.9649   $161.96   $161.95   $162.00  
  Purchase #2 $62.98   12.611%   $70.9224   $70.92   $70.90   $70.90  
  Purchase #3 $50.97   4.453%   $53.2397   $53.24   $53.25   $53.20  
  Purchase #4 $60.29   11.237%   $67.0648   $67.06   $67.05   $67.10  
  Purchase #5 $22.71   4.365%   $23.7013   $23.70   $23.70   $23.70  
  Purchase #6 $188.82   6.481%   $201.0574   $201.06   $201.05   $201.10  
  Purchase #7 $168.29   11.170%   $187.088   $187.09   $187.10   $187.10  
  7 purchase totals = $702.51       $765.0385   $765.03   $765.00   $765.10