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 $236.68   13.132%   $267.7608   $267.76   $267.75   $267.80  
  Purchase #2 $152.71   13.488%   $173.3075   $173.31   $173.30   $173.30  
  Purchase #3 $92.50   5.449%   $97.5403   $97.54   $97.55   $97.50  
  Purchase #4 $178.62   5.165%   $187.8457   $187.85   $187.85   $187.80  
  Purchase #5 $147.96   11.798%   $165.4163   $165.42   $165.40   $165.40  
  Purchase #6 $61.37   4.482%   $64.1206   $64.12   $64.10   $64.10  
  Purchase #7 $161.95   3.619%   $167.811   $167.81   $167.80   $167.80  
  7 purchase totals = $1,031.79       $1,123.8022   $1,123.81   $1,123.75   $1,123.70