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 $105.41   4.245%   $109.8847   $109.88   $109.90   $109.90  
  Purchase #2 $230.60   4.717%   $241.4774   $241.48   $241.50   $241.50  
  Purchase #3 $165.30   9.362%   $180.7754   $180.78   $180.80   $180.80  
  Purchase #4 $42.86   7.613%   $46.1229   $46.12   $46.10   $46.10  
  Purchase #5 $169.33   7.698%   $182.365   $182.37   $182.35   $182.40  
  Purchase #6 $6.75   9.764%   $7.4091   $7.41   $7.40   $7.40  
  Purchase #7 $148.86   8.212%   $161.0844   $161.08   $161.10   $161.10  
  7 purchase totals = $869.11       $929.1189   $929.12   $929.15   $929.20