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 $59.36   10.697%   $65.7097   $65.71   $65.70   $65.70  
  Purchase #2 $124.70   6.707%   $133.0636   $133.06   $133.05   $133.10  
  Purchase #3 $180.57   7.489%   $194.0929   $194.09   $194.10   $194.10  
  Purchase #4 $184.37   9.249%   $201.4224   $201.42   $201.40   $201.40  
  Purchase #5 $174.27   7.270%   $186.9394   $186.94   $186.95   $186.90  
  Purchase #6 $58.41   11.429%   $65.0857   $65.09   $65.10   $65.10  
  Purchase #7 $11.55   11.212%   $12.845   $12.85   $12.85   $12.80  
  7 purchase totals = $793.23       $859.1587   $859.16   $859.15   $859.10