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 $246.42   10.104%   $271.3183   $271.32   $271.30   $271.30  
  Purchase #2 $118.47   13.406%   $134.3521   $134.35   $134.35   $134.40  
  Purchase #3 $113.60   10.529%   $125.5609   $125.56   $125.55   $125.60  
  Purchase #4 $146.74   4.363%   $153.1423   $153.14   $153.15   $153.10  
  Purchase #5 $91.62   11.474%   $102.1325   $102.13   $102.15   $102.10  
  Purchase #6 $244.86   13.214%   $277.2158   $277.22   $277.20   $277.20  
  Purchase #7 $26.42   12.583%   $29.7444   $29.74   $29.75   $29.70  
  7 purchase totals = $988.13       $1,093.4663   $1,093.46   $1,093.45   $1,093.40