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 $246.52   8.566%   $267.6369   $267.64   $267.65   $267.60  
  Purchase #2 $23.33   7.814%   $25.153   $25.15   $25.15   $25.20  
  Purchase #3 $126.27   13.304%   $143.069   $143.07   $143.05   $143.10  
  Purchase #4 $118.36   11.815%   $132.3442   $132.34   $132.35   $132.30  
  Purchase #5 $28.39   5.599%   $29.9796   $29.98   $30.00   $30.00  
  Purchase #6 $155.36   12.484%   $174.7551   $174.76   $174.75   $174.80  
  Purchase #7 $173.55   6.110%   $184.1539   $184.15   $184.15   $184.20  
  7 purchase totals = $871.78       $957.0917   $957.09   $957.10   $957.20