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 $73.85   11.396%   $82.2659   $82.27   $82.25   $82.30  
  Purchase #2 $136.38   13.387%   $154.6372   $154.64   $154.65   $154.60  
  Purchase #3 $205.85   12.772%   $232.1412   $232.14   $232.15   $232.10  
  Purchase #4 $148.31   7.438%   $159.3413   $159.34   $159.35   $159.30  
  Purchase #5 $64.91   6.600%   $69.1941   $69.19   $69.20   $69.20  
  Purchase #6 $207.33   11.437%   $231.0423   $231.04   $231.05   $231.00  
  Purchase #7 $213.75   5.597%   $225.7136   $225.71   $225.70   $225.70  
  7 purchase totals = $1,050.38       $1,154.3356   $1,154.33   $1,154.35   $1,154.20