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 $208.33   12.382%   $234.1254   $234.13   $234.15   $234.10  
  Purchase #2 $44.30   5.134%   $46.5744   $46.57   $46.55   $46.60  
  Purchase #3 $190.49   10.497%   $210.4857   $210.49   $210.50   $210.50  
  Purchase #4 $187.76   3.604%   $194.5269   $194.53   $194.55   $194.50  
  Purchase #5 $111.64   8.629%   $121.2734   $121.27   $121.25   $121.30  
  Purchase #6 $45.61   10.361%   $50.3357   $50.34   $50.35   $50.30  
  Purchase #7 $158.83   6.413%   $169.0158   $169.02   $169.00   $169.00  
  7 purchase totals = $946.96       $1,026.3373   $1,026.35   $1,026.35   $1,026.30