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 $124.84   5.751%   $132.0195   $132.02   $132.00   $132.00  
  Purchase #2 $86.48   3.541%   $89.5423   $89.54   $89.55   $89.50  
  Purchase #3 $247.46   11.554%   $276.0515   $276.05   $276.05   $276.10  
  Purchase #4 $196.87   4.550%   $205.8276   $205.83   $205.85   $205.80  
  Purchase #5 $206.25   9.280%   $225.39   $225.39   $225.40   $225.40  
  Purchase #6 $180.80   7.600%   $194.5408   $194.54   $194.55   $194.50  
  Purchase #7 $141.94   5.614%   $149.9085   $149.91   $149.90   $149.90  
  7 purchase totals = $1,184.64       $1,273.2802   $1,273.28   $1,273.30   $1,273.20