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 $49.52   6.793%   $52.8839   $52.88   $52.90   $52.90  
  Purchase #2 $88.26   7.196%   $94.6112   $94.61   $94.60   $94.60  
  Purchase #3 $108.71   6.868%   $116.1762   $116.18   $116.20   $116.20  
  Purchase #4 $225.60   7.122%   $241.6672   $241.67   $241.65   $241.70  
  Purchase #5 $39.49   11.508%   $44.0345   $44.03   $44.05   $44.00  
  Purchase #6 $125.31   8.149%   $135.5215   $135.52   $135.50   $135.50  
  Purchase #7 $30.39   4.535%   $31.7682   $31.77   $31.75   $31.80  
  7 purchase totals = $667.28       $716.6627   $716.66   $716.65   $716.70