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 $91.29   7.291%   $97.946   $97.95   $97.95   $97.90  
  Purchase #2 $38.34   6.151%   $40.6983   $40.70   $40.70   $40.70  
  Purchase #3 $235.42   9.157%   $256.9774   $256.98   $257.00   $257.00  
  Purchase #4 $163.98   13.340%   $185.8549   $185.85   $185.85   $185.90  
  Purchase #5 $125.78   7.149%   $134.772   $134.77   $134.75   $134.80  
  Purchase #6 $176.78   9.720%   $193.963   $193.96   $193.95   $194.00  
  Purchase #7 $133.35   12.505%   $150.0254   $150.03   $150.05   $150.00  
  7 purchase totals = $964.94       $1,060.2370   $1,060.24   $1,060.25   $1,060.30