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 $97.33   4.122%   $101.3419   $101.34   $101.35   $101.30  
  Purchase #2 $184.64   10.731%   $204.4537   $204.45   $204.45   $204.50  
  Purchase #3 $191.85   13.771%   $218.2697   $218.27   $218.25   $218.30  
  Purchase #4 $25.76   3.179%   $26.5789   $26.58   $26.60   $26.60  
  Purchase #5 $186.87   9.833%   $205.2449   $205.24   $205.25   $205.20  
  Purchase #6 $153.86   10.661%   $170.263   $170.26   $170.25   $170.30  
  Purchase #7 $9.34   8.757%   $10.1579   $10.16   $10.15   $10.20  
  7 purchase totals = $849.65       $936.3100   $936.30   $936.30   $936.40