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 $241.98   8.650%   $262.9113   $262.91   $262.90   $262.90  
  Purchase #2 $13.62   7.622%   $14.6581   $14.66   $14.65   $14.70  
  Purchase #3 $112.40   12.191%   $126.1027   $126.10   $126.10   $126.10  
  Purchase #4 $112.93   3.210%   $116.5551   $116.56   $116.55   $116.60  
  Purchase #5 $202.62   10.419%   $223.731   $223.73   $223.75   $223.70  
  Purchase #6 $222.87   9.295%   $243.5858   $243.59   $243.60   $243.60  
  Purchase #7 $132.39   13.847%   $150.722   $150.72   $150.70   $150.70  
  7 purchase totals = $1,038.81       $1,138.2660   $1,138.27   $1,138.25   $1,138.30