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 $239.81   8.797%   $260.9061   $260.91   $260.90   $260.90  
  Purchase #2 $86.49   7.737%   $93.1817   $93.18   $93.20   $93.20  
  Purchase #3 $220.90   11.386%   $246.0517   $246.05   $246.05   $246.10  
  Purchase #4 $235.92   13.534%   $267.8494   $267.85   $267.85   $267.80  
  Purchase #5 $89.55   11.649%   $99.9817   $99.98   $100.00   $100.00  
  Purchase #6 $242.35   12.514%   $272.6777   $272.68   $272.70   $272.70  
  Purchase #7 $29.91   12.484%   $33.644   $33.64   $33.65   $33.60  
  7 purchase totals = $1,144.93       $1,274.2923   $1,274.29   $1,274.35   $1,274.30