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 $45.29   10.288%   $49.9494   $49.95   $49.95   $49.90  
  Purchase #2 $212.26   13.517%   $240.9512   $240.95   $240.95   $241.00  
  Purchase #3 $150.77   8.524%   $163.6216   $163.62   $163.60   $163.60  
  Purchase #4 $58.78   9.403%   $64.3071   $64.31   $64.30   $64.30  
  Purchase #5 $5.49   13.844%   $6.25   $6.25   $6.25   $6.30  
  Purchase #6 $203.47   13.302%   $230.5356   $230.54   $230.55   $230.50  
  Purchase #7 $175.90   9.645%   $192.8656   $192.87   $192.85   $192.90  
  7 purchase totals = $851.96       $948.4805   $948.49   $948.45   $948.50