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 $209.83   11.865%   $234.7263   $234.73   $234.75   $234.70  
  Purchase #2 $250.32   5.848%   $264.9587   $264.96   $264.95   $265.00  
  Purchase #3 $83.33   5.168%   $87.6365   $87.64   $87.65   $87.60  
  Purchase #4 $137.38   9.491%   $150.4187   $150.42   $150.40   $150.40  
  Purchase #5 $110.60   13.684%   $125.7345   $125.73   $125.75   $125.70  
  Purchase #6 $163.91   7.629%   $176.4147   $176.41   $176.40   $176.40  
  Purchase #7 $141.68   10.409%   $156.4275   $156.43   $156.45   $156.40  
  7 purchase totals = $1,097.05       $1,196.3169   $1,196.32   $1,196.35   $1,196.20