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 $209.41   6.807%   $223.6645   $223.66   $223.65   $223.70  
  Purchase #2 $151.46   7.449%   $162.7423   $162.74   $162.75   $162.70  
  Purchase #3 $210.66   4.708%   $220.5779   $220.58   $220.60   $220.60  
  Purchase #4 $202.42   11.158%   $225.006   $225.01   $225.00   $225.00  
  Purchase #5 $135.83   4.374%   $141.7712   $141.77   $141.75   $141.80  
  Purchase #6 $149.38   5.331%   $157.3434   $157.34   $157.35   $157.30  
  Purchase #7 $211.85   7.555%   $227.8553   $227.86   $227.85   $227.90  
  7 purchase totals = $1,271.01       $1,358.9606   $1,358.96   $1,358.95   $1,359.00