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 $129.25   13.148%   $146.2438   $146.24   $146.25   $146.20  
  Purchase #2 $59.78   11.495%   $66.6517   $66.65   $66.65   $66.70  
  Purchase #3 $165.96   10.753%   $183.8057   $183.81   $183.80   $183.80  
  Purchase #4 $188.44   9.294%   $205.9536   $205.95   $205.95   $206.00  
  Purchase #5 $220.78   5.564%   $233.0642   $233.06   $233.05   $233.10  
  Purchase #6 $140.73   7.465%   $151.2355   $151.24   $151.25   $151.20  
  Purchase #7 $26.94   9.698%   $29.5526   $29.55   $29.55   $29.60  
  7 purchase totals = $931.88       $1,016.5071   $1,016.50   $1,016.50   $1,016.60