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 $84.83   10.671%   $93.8822   $93.88   $93.90   $93.90  
  Purchase #2 $11.44   3.534%   $11.8443   $11.84   $11.85   $11.80  
  Purchase #3 $48.94   10.252%   $53.9573   $53.96   $53.95   $54.00  
  Purchase #4 $41.27   11.389%   $45.9702   $45.97   $45.95   $46.00  
  Purchase #5 $223.42   8.641%   $242.7257   $242.73   $242.75   $242.70  
  Purchase #6 $44.92   10.713%   $49.7323   $49.73   $49.75   $49.70  
  Purchase #7 $111.83   6.342%   $118.9223   $118.92   $118.90   $118.90  
  7 purchase totals = $566.65       $617.0343   $617.03   $617.05   $617.00