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 $57.98   8.857%   $63.1153   $63.12   $63.10   $63.10  
  Purchase #2 $14.56   6.576%   $15.5175   $15.52   $15.50   $15.50  
  Purchase #3 $108.33   11.163%   $120.4229   $120.42   $120.40   $120.40  
  Purchase #4 $211.77   12.327%   $237.8749   $237.87   $237.85   $237.90  
  Purchase #5 $187.59   12.158%   $210.3972   $210.40   $210.40   $210.40  
  Purchase #6 $180.90   10.295%   $199.5237   $199.52   $199.50   $199.50  
  Purchase #7 $234.87   5.811%   $248.5183   $248.52   $248.50   $248.50  
  7 purchase totals = $996.00       $1,095.3698   $1,095.37   $1,095.25   $1,095.30