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 $201.29   12.200%   $225.8474   $225.85   $225.85   $225.80  
  Purchase #2 $159.88   5.732%   $169.0443   $169.04   $169.05   $169.00  
  Purchase #3 $49.29   13.536%   $55.9619   $55.96   $55.95   $56.00  
  Purchase #4 $128.46   9.705%   $140.927   $140.93   $140.95   $140.90  
  Purchase #5 $171.78   8.110%   $185.7114   $185.71   $185.70   $185.70  
  Purchase #6 $213.80   8.635%   $232.2616   $232.26   $232.25   $232.30  
  Purchase #7 $107.77   5.289%   $113.47   $113.47   $113.45   $113.50  
  7 purchase totals = $1,032.27       $1,123.2236   $1,123.22   $1,123.20   $1,123.20