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 $226.41   7.454%   $243.2866   $243.29   $243.30   $243.30  
  Purchase #2 $96.88   6.380%   $103.0609   $103.06   $103.05   $103.10  
  Purchase #3 $103.71   7.623%   $111.6158   $111.62   $111.60   $111.60  
  Purchase #4 $60.65   10.207%   $66.8405   $66.84   $66.85   $66.80  
  Purchase #5 $74.47   10.351%   $82.1784   $82.18   $82.20   $82.20  
  Purchase #6 $201.95   11.464%   $225.1015   $225.10   $225.10   $225.10  
  Purchase #7 $49.41   11.358%   $55.022   $55.02   $55.00   $55.00  
  7 purchase totals = $813.48       $887.1057   $887.11   $887.10   $887.10