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 $206.62   3.237%   $213.3083   $213.31   $213.30   $213.30  
  Purchase #2 $98.86   3.743%   $102.5603   $102.56   $102.55   $102.60  
  Purchase #3 $53.87   6.137%   $57.176   $57.18   $57.20   $57.20  
  Purchase #4 $157.79   12.631%   $177.7205   $177.72   $177.70   $177.70  
  Purchase #5 $13.62   8.630%   $14.7954   $14.80   $14.80   $14.80  
  Purchase #6 $175.47   12.497%   $197.3985   $197.40   $197.40   $197.40  
  Purchase #7 $56.32   9.769%   $61.8219   $61.82   $61.80   $61.80  
  7 purchase totals = $762.55       $824.7809   $824.79   $824.75   $824.80