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 $65.87   11.281%   $73.3008   $73.30   $73.30   $73.30  
  Purchase #2 $110.45   5.635%   $116.6739   $116.67   $116.65   $116.70  
  Purchase #3 $201.84   4.414%   $210.7492   $210.75   $210.75   $210.70  
  Purchase #4 $40.61   9.104%   $44.3071   $44.31   $44.30   $44.30  
  Purchase #5 $100.54   6.582%   $107.1575   $107.16   $107.15   $107.20  
  Purchase #6 $189.28   11.568%   $211.1759   $211.18   $211.20   $211.20  
  Purchase #7 $12.63   6.455%   $13.4453   $13.45   $13.45   $13.40  
  7 purchase totals = $721.22       $776.8097   $776.82   $776.80   $776.80