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 $203.63   3.120%   $209.9833   $209.98   $210.00   $210.00  
  Purchase #2 $69.57   6.387%   $74.0134   $74.01   $74.00   $74.00  
  Purchase #3 $117.98   9.299%   $128.951   $128.95   $128.95   $129.00  
  Purchase #4 $142.79   11.782%   $159.6135   $159.61   $159.60   $159.60  
  Purchase #5 $161.88   8.109%   $175.0068   $175.01   $175.00   $175.00  
  Purchase #6 $238.26   11.269%   $265.1095   $265.11   $265.10   $265.10  
  Purchase #7 $65.25   7.272%   $69.995   $70.00   $70.00   $70.00  
  7 purchase totals = $999.36       $1,082.6725   $1,082.67   $1,082.65   $1,082.70