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 $52.52   12.225%   $58.9406   $58.94   $58.95   $58.90  
  Purchase #2 $20.57   3.114%   $21.2105   $21.21   $21.20   $21.20  
  Purchase #3 $40.68   5.832%   $43.0525   $43.05   $43.05   $43.10  
  Purchase #4 $21.59   5.600%   $22.799   $22.80   $22.80   $22.80  
  Purchase #5 $239.56   6.597%   $255.3638   $255.36   $255.35   $255.40  
  Purchase #6 $220.37   11.673%   $246.0938   $246.09   $246.10   $246.10  
  Purchase #7 $228.80   8.245%   $247.6646   $247.66   $247.65   $247.70  
  7 purchase totals = $824.09       $895.1248   $895.11   $895.10   $895.20