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 $32.89   7.178%   $35.2508   $35.25   $35.25   $35.30  
  Purchase #2 $23.86   9.397%   $26.1021   $26.10   $26.10   $26.10  
  Purchase #3 $91.55   5.521%   $96.6045   $96.60   $96.60   $96.60  
  Purchase #4 $95.75   13.383%   $108.5642   $108.56   $108.55   $108.60  
  Purchase #5 $126.70   8.572%   $137.5607   $137.56   $137.55   $137.60  
  Purchase #6 $180.37   13.570%   $204.8462   $204.85   $204.85   $204.80  
  Purchase #7 $241.26   11.342%   $268.6237   $268.62   $268.60   $268.60  
  7 purchase totals = $792.38       $877.5522   $877.54   $877.50   $877.60