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 $55.88   10.324%   $61.6491   $61.65   $61.65   $61.60  
  Purchase #2 $97.32   13.831%   $110.7803   $110.78   $110.80   $110.80  
  Purchase #3 $118.92   8.388%   $128.895   $128.90   $128.90   $128.90  
  Purchase #4 $6.47   10.156%   $7.1271   $7.13   $7.15   $7.10  
  Purchase #5 $88.97   4.261%   $92.761   $92.76   $92.75   $92.80  
  Purchase #6 $223.88   7.654%   $241.0158   $241.02   $241.00   $241.00  
  Purchase #7 $40.26   12.329%   $45.2237   $45.22   $45.20   $45.20  
  7 purchase totals = $631.70       $687.4520   $687.46   $687.45   $687.40