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 $223.41   11.431%   $248.948   $248.95   $248.95   $248.90  
  Purchase #2 $102.80   13.733%   $116.9175   $116.92   $116.90   $116.90  
  Purchase #3 $108.55   13.814%   $123.5451   $123.55   $123.55   $123.50  
  Purchase #4 $57.89   9.314%   $63.2819   $63.28   $63.30   $63.30  
  Purchase #5 $102.31   5.249%   $107.6803   $107.68   $107.70   $107.70  
  Purchase #6 $224.52   5.286%   $236.3881   $236.39   $236.40   $236.40  
  Purchase #7 $150.47   11.576%   $167.8884   $167.89   $167.90   $167.90  
  7 purchase totals = $969.95       $1,064.6493   $1,064.66   $1,064.70   $1,064.60