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 $236.98   12.823%   $267.3679   $267.37   $267.35   $267.40  
  Purchase #2 $164.82   9.623%   $180.6806   $180.68   $180.70   $180.70  
  Purchase #3 $232.31   10.592%   $256.9163   $256.92   $256.90   $256.90  
  Purchase #4 $229.75   10.769%   $254.4918   $254.49   $254.50   $254.50  
  Purchase #5 $238.28   6.335%   $253.375   $253.38   $253.40   $253.40  
  Purchase #6 $64.45   7.534%   $69.3057   $69.31   $69.30   $69.30  
  Purchase #7 $88.51   10.185%   $97.5247   $97.52   $97.50   $97.50  
  7 purchase totals = $1,255.10       $1,379.6620   $1,379.67   $1,379.65   $1,379.70