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 $136.71   10.641%   $151.2573   $151.26   $151.25   $151.30  
  Purchase #2 $71.80   10.360%   $79.2385   $79.24   $79.25   $79.20  
  Purchase #3 $167.90   3.375%   $173.5666   $173.57   $173.55   $173.60  
  Purchase #4 $175.64   9.224%   $191.841   $191.84   $191.85   $191.80  
  Purchase #5 $106.25   12.554%   $119.5886   $119.59   $119.60   $119.60  
  Purchase #6 $128.32   11.836%   $143.508   $143.51   $143.50   $143.50  
  Purchase #7 $173.65   11.541%   $193.6909   $193.69   $193.70   $193.70  
  7 purchase totals = $960.27       $1,052.6909   $1,052.70   $1,052.70   $1,052.70