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 $191.76   11.618%   $214.0387   $214.04   $214.05   $214.00  
  Purchase #2 $214.58   8.558%   $232.9438   $232.94   $232.95   $232.90  
  Purchase #3 $31.53   5.493%   $33.2619   $33.26   $33.25   $33.30  
  Purchase #4 $89.96   4.221%   $93.7572   $93.76   $93.75   $93.80  
  Purchase #5 $104.64   7.317%   $112.2965   $112.30   $112.30   $112.30  
  Purchase #6 $24.26   6.698%   $25.8849   $25.88   $25.90   $25.90  
  Purchase #7 $146.71   11.243%   $163.2046   $163.20   $163.20   $163.20  
  7 purchase totals = $803.44       $875.3876   $875.38   $875.40   $875.40