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 $231.43   7.129%   $247.9286   $247.93   $247.95   $247.90  
  Purchase #2 $87.94   10.249%   $96.953   $96.95   $96.95   $97.00  
  Purchase #3 $130.65   10.592%   $144.4884   $144.49   $144.50   $144.50  
  Purchase #4 $91.65   8.732%   $99.6529   $99.65   $99.65   $99.70  
  Purchase #5 $102.34   10.801%   $113.3937   $113.39   $113.40   $113.40  
  Purchase #6 $211.47   12.693%   $238.3119   $238.31   $238.30   $238.30  
  Purchase #7 $89.76   5.823%   $94.9867   $94.99   $95.00   $95.00  
  7 purchase totals = $945.24       $1,035.7152   $1,035.71   $1,035.75   $1,035.80