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 $41.75   11.146%   $46.4035   $46.40   $46.40   $46.40  
  Purchase #2 $133.84   13.305%   $151.6474   $151.65   $151.65   $151.60  
  Purchase #3 $156.93   10.191%   $172.9227   $172.92   $172.90   $172.90  
  Purchase #4 $39.78   12.755%   $44.8539   $44.85   $44.85   $44.90  
  Purchase #5 $206.92   11.226%   $230.1488   $230.15   $230.15   $230.10  
  Purchase #6 $8.60   13.717%   $9.7797   $9.78   $9.80   $9.80  
  Purchase #7 $184.84   5.147%   $194.3537   $194.35   $194.35   $194.40  
  7 purchase totals = $772.66       $850.1097   $850.10   $850.10   $850.10