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 $58.43   11.318%   $65.0431   $65.04   $65.05   $65.00  
  Purchase #2 $138.41   12.277%   $155.4026   $155.40   $155.40   $155.40  
  Purchase #3 $245.85   5.153%   $258.5187   $258.52   $258.50   $258.50  
  Purchase #4 $210.59   7.823%   $227.0645   $227.06   $227.05   $227.10  
  Purchase #5 $235.40   13.566%   $267.3344   $267.33   $267.35   $267.30  
  Purchase #6 $91.69   13.412%   $103.9875   $103.99   $104.00   $104.00  
  Purchase #7 $248.67   3.298%   $256.8711   $256.87   $256.85   $256.90  
  7 purchase totals = $1,229.04       $1,334.2219   $1,334.21   $1,334.20   $1,334.20