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 $86.65   12.614%   $97.58   $97.58   $97.60   $97.60  
  Purchase #2 $121.27   5.275%   $127.667   $127.67   $127.65   $127.70  
  Purchase #3 $130.58   10.785%   $144.6631   $144.66   $144.65   $144.70  
  Purchase #4 $68.77   11.473%   $76.66   $76.66   $76.65   $76.70  
  Purchase #5 $204.82   11.561%   $228.4992   $228.50   $228.50   $228.50  
  Purchase #6 $246.56   4.446%   $257.5221   $257.52   $257.50   $257.50  
  Purchase #7 $15.37   8.411%   $16.6628   $16.66   $16.65   $16.70  
  7 purchase totals = $874.02       $949.2542   $949.25   $949.20   $949.40