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 $64.65   3.228%   $66.7369   $66.74   $66.75   $66.70  
  Purchase #2 $174.65   9.791%   $191.75   $191.75   $191.75   $191.80  
  Purchase #3 $243.29   3.827%   $252.6007   $252.60   $252.60   $252.60  
  Purchase #4 $199.78   4.139%   $208.0489   $208.05   $208.05   $208.00  
  Purchase #5 $91.67   8.680%   $99.627   $99.63   $99.65   $99.60  
  Purchase #6 $179.47   12.793%   $202.4296   $202.43   $202.45   $202.40  
  Purchase #7 $196.51   4.737%   $205.8187   $205.82   $205.80   $205.80  
  7 purchase totals = $1,150.02       $1,227.0118   $1,227.02   $1,227.05   $1,226.90