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 $34.73   6.361%   $36.9392   $36.94   $36.95   $36.90  
  Purchase #2 $182.92   11.215%   $203.4345   $203.43   $203.45   $203.40  
  Purchase #3 $210.56   5.462%   $222.0608   $222.06   $222.05   $222.10  
  Purchase #4 $199.47   13.665%   $226.7276   $226.73   $226.75   $226.70  
  Purchase #5 $130.66   10.831%   $144.8118   $144.81   $144.80   $144.80  
  Purchase #6 $19.58   5.825%   $20.7205   $20.72   $20.70   $20.70  
  Purchase #7 $195.57   8.273%   $211.7495   $211.75   $211.75   $211.70  
  7 purchase totals = $973.49       $1,066.4439   $1,066.44   $1,066.45   $1,066.30