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 $65.90   4.721%   $69.0111   $69.01   $69.00   $69.00  
  Purchase #2 $48.86   10.279%   $53.8823   $53.88   $53.90   $53.90  
  Purchase #3 $211.70   11.289%   $235.5988   $235.60   $235.60   $235.60  
  Purchase #4 $181.58   12.340%   $203.987   $203.99   $204.00   $204.00  
  Purchase #5 $84.88   4.784%   $88.9407   $88.94   $88.95   $88.90  
  Purchase #6 $31.94   12.271%   $35.8594   $35.86   $35.85   $35.90  
  Purchase #7 $110.26   11.287%   $122.705   $122.71   $122.70   $122.70  
  7 purchase totals = $735.12       $809.9843   $809.99   $810.00   $810.00