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 $29.69   13.594%   $33.7261   $33.73   $33.75   $33.70  
  Purchase #2 $117.71   11.442%   $131.1784   $131.18   $131.20   $131.20  
  Purchase #3 $145.63   12.390%   $163.6736   $163.67   $163.65   $163.70  
  Purchase #4 $175.27   12.568%   $197.2979   $197.30   $197.30   $197.30  
  Purchase #5 $113.90   10.749%   $126.1431   $126.14   $126.15   $126.10  
  Purchase #6 $176.43   12.773%   $198.9654   $198.97   $198.95   $199.00  
  Purchase #7 $149.39   8.201%   $161.6415   $161.64   $161.65   $161.60  
  7 purchase totals = $908.02       $1,012.6260   $1,012.63   $1,012.65   $1,012.60