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 $196.78   7.195%   $210.9383   $210.94   $210.95   $210.90  
  Purchase #2 $96.92   5.510%   $102.2603   $102.26   $102.25   $102.30  
  Purchase #3 $143.88   4.738%   $150.697   $150.70   $150.70   $150.70  
  Purchase #4 $227.80   12.581%   $256.4595   $256.46   $256.45   $256.50  
  Purchase #5 $22.83   3.705%   $23.6759   $23.68   $23.70   $23.70  
  Purchase #6 $50.70   7.273%   $54.3874   $54.39   $54.40   $54.40  
  Purchase #7 $195.72   4.553%   $204.6311   $204.63   $204.65   $204.60  
  7 purchase totals = $934.63       $1,003.0495   $1,003.06   $1,003.10   $1,003.10