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 $72.53   3.409%   $75.0025   $75.00   $75.00   $75.00  
  Purchase #2 $207.32   13.341%   $234.9786   $234.98   $235.00   $235.00  
  Purchase #3 $106.37   6.860%   $113.667   $113.67   $113.65   $113.70  
  Purchase #4 $112.95   5.176%   $118.7963   $118.80   $118.80   $118.80  
  Purchase #5 $199.99   7.284%   $214.5573   $214.56   $214.55   $214.60  
  Purchase #6 $177.83   8.179%   $192.3747   $192.37   $192.35   $192.40  
  Purchase #7 $6.48   5.473%   $6.8347   $6.83   $6.85   $6.80  
  7 purchase totals = $883.47       $956.2111   $956.21   $956.20   $956.30