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 $92.93   5.148%   $97.714   $97.71   $97.70   $97.70  
  Purchase #2 $231.99   10.308%   $255.9035   $255.90   $255.90   $255.90  
  Purchase #3 $174.45   13.260%   $197.5821   $197.58   $197.60   $197.60  
  Purchase #4 $244.47   9.799%   $268.4256   $268.43   $268.45   $268.40  
  Purchase #5 $222.95   6.108%   $236.5678   $236.57   $236.55   $236.60  
  Purchase #6 $113.81   9.801%   $124.9645   $124.96   $124.95   $125.00  
  Purchase #7 $217.72   4.169%   $226.7967   $226.80   $226.80   $226.80  
  7 purchase totals = $1,298.32       $1,407.9542   $1,407.95   $1,407.95   $1,408.00