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 $42.69   8.717%   $46.4113   $46.41   $46.40   $46.40  
  Purchase #2 $142.97   6.613%   $152.4246   $152.42   $152.40   $152.40  
  Purchase #3 $202.82   9.256%   $221.593   $221.59   $221.60   $221.60  
  Purchase #4 $246.26   6.782%   $262.9614   $262.96   $262.95   $263.00  
  Purchase #5 $118.30   5.195%   $124.4457   $124.45   $124.45   $124.40  
  Purchase #6 $161.60   11.647%   $180.4216   $180.42   $180.40   $180.40  
  Purchase #7 $169.75   11.411%   $189.1202   $189.12   $189.10   $189.10  
  7 purchase totals = $1,084.39       $1,177.3778   $1,177.37   $1,177.30   $1,177.30