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 $223.96   10.808%   $248.1656   $248.17   $248.15   $248.20  
  Purchase #2 $63.27   7.509%   $68.0209   $68.02   $68.00   $68.00  
  Purchase #3 $94.70   10.574%   $104.7136   $104.71   $104.70   $104.70  
  Purchase #4 $195.96   10.849%   $217.2197   $217.22   $217.20   $217.20  
  Purchase #5 $189.46   6.284%   $201.3657   $201.37   $201.35   $201.40  
  Purchase #6 $104.79   3.242%   $108.1873   $108.19   $108.20   $108.20  
  Purchase #7 $153.94   12.829%   $173.689   $173.69   $173.70   $173.70  
  7 purchase totals = $1,026.08       $1,121.3618   $1,121.37   $1,121.30   $1,121.40