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 $84.59   8.808%   $92.0407   $92.04   $92.05   $92.00  
  Purchase #2 $174.81   3.554%   $181.0227   $181.02   $181.00   $181.00  
  Purchase #3 $250.85   9.347%   $274.2969   $274.30   $274.30   $274.30  
  Purchase #4 $214.34   7.137%   $229.6374   $229.64   $229.65   $229.60  
  Purchase #5 $125.92   7.415%   $135.257   $135.26   $135.25   $135.30  
  Purchase #6 $82.54   5.791%   $87.3199   $87.32   $87.30   $87.30  
  Purchase #7 $159.45   9.718%   $174.9454   $174.95   $174.95   $174.90  
  7 purchase totals = $1,092.50       $1,174.5200   $1,174.53   $1,174.50   $1,174.40