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 $188.98   9.448%   $206.8348   $206.83   $206.85   $206.80  
  Purchase #2 $162.35   7.507%   $174.5376   $174.54   $174.55   $174.50  
  Purchase #3 $124.84   4.676%   $130.6775   $130.68   $130.70   $130.70  
  Purchase #4 $65.91   5.682%   $69.655   $69.66   $69.65   $69.70  
  Purchase #5 $99.37   6.708%   $106.0357   $106.04   $106.05   $106.00  
  Purchase #6 $133.38   12.679%   $150.2913   $150.29   $150.30   $150.30  
  Purchase #7 $161.69   7.470%   $173.7682   $173.77   $173.75   $173.80  
  7 purchase totals = $936.52       $1,011.8001   $1,011.81   $1,011.85   $1,011.80