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 $122.62   9.814%   $134.6539   $134.65   $134.65   $134.70  
  Purchase #2 $219.58   4.136%   $228.6618   $228.66   $228.65   $228.70  
  Purchase #3 $81.87   6.261%   $86.9959   $87.00   $87.00   $87.00  
  Purchase #4 $78.50   4.485%   $82.0207   $82.02   $82.00   $82.00  
  Purchase #5 $174.80   5.742%   $184.837   $184.84   $184.85   $184.80  
  Purchase #6 $49.42   11.242%   $54.9758   $54.98   $55.00   $55.00  
  Purchase #7 $41.82   6.293%   $44.4517   $44.45   $44.45   $44.50  
  7 purchase totals = $768.61       $816.5968   $816.60   $816.60   $816.70