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 $211.48   12.662%   $238.2576   $238.26   $238.25   $238.30  
  Purchase #2 $26.38   11.499%   $29.4134   $29.41   $29.40   $29.40  
  Purchase #3 $200.81   9.635%   $220.158   $220.16   $220.15   $220.20  
  Purchase #4 $182.67   9.395%   $199.8318   $199.83   $199.85   $199.80  
  Purchase #5 $14.68   5.764%   $15.5262   $15.53   $15.55   $15.50  
  Purchase #6 $170.89   10.785%   $189.3205   $189.32   $189.30   $189.30  
  Purchase #7 $144.74   5.720%   $153.0191   $153.02   $153.00   $153.00  
  7 purchase totals = $951.65       $1,045.5266   $1,045.53   $1,045.50   $1,045.50