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 $144.72   11.253%   $161.0053   $161.01   $161.00   $161.00  
  Purchase #2 $144.46   7.751%   $155.6571   $155.66   $155.65   $155.70  
  Purchase #3 $49.94   6.727%   $53.2995   $53.30   $53.30   $53.30  
  Purchase #4 $235.34   9.465%   $257.6149   $257.61   $257.60   $257.60  
  Purchase #5 $170.99   11.612%   $190.8454   $190.85   $190.85   $190.80  
  Purchase #6 $75.92   8.213%   $82.1553   $82.16   $82.15   $82.20  
  Purchase #7 $78.90   9.849%   $86.6709   $86.67   $86.65   $86.70  
  7 purchase totals = $900.27       $987.2484   $987.26   $987.20   $987.30