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 $61.38   12.407%   $68.9954   $69.00   $69.00   $69.00  
  Purchase #2 $136.99   10.788%   $151.7685   $151.77   $151.75   $151.80  
  Purchase #3 $240.56   8.324%   $260.5842   $260.58   $260.60   $260.60  
  Purchase #4 $159.85   6.123%   $169.6376   $169.64   $169.65   $169.60  
  Purchase #5 $36.59   12.205%   $41.0558   $41.06   $41.05   $41.10  
  Purchase #6 $60.82   5.536%   $64.187   $64.19   $64.20   $64.20  
  Purchase #7 $123.29   6.814%   $131.691   $131.69   $131.70   $131.70  
  7 purchase totals = $819.48       $887.9195   $887.93   $887.95   $888.00