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 $84.83   13.519%   $96.2982   $96.30   $96.30   $96.30  
  Purchase #2 $225.72   8.233%   $244.3035   $244.30   $244.30   $244.30  
  Purchase #3 $90.89   3.122%   $93.7276   $93.73   $93.75   $93.70  
  Purchase #4 $224.95   12.741%   $253.6109   $253.61   $253.60   $253.60  
  Purchase #5 $181.64   12.786%   $204.8645   $204.86   $204.85   $204.90  
  Purchase #6 $129.81   6.628%   $138.4138   $138.41   $138.40   $138.40  
  Purchase #7 $113.59   7.528%   $122.1411   $122.14   $122.15   $122.10  
  7 purchase totals = $1,051.43       $1,153.3596   $1,153.35   $1,153.35   $1,153.30