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 $206.25   11.832%   $230.6535   $230.65   $230.65   $230.70  
  Purchase #2 $50.39   8.239%   $54.5416   $54.54   $54.55   $54.50  
  Purchase #3 $55.50   11.442%   $61.8503   $61.85   $61.85   $61.90  
  Purchase #4 $132.28   8.686%   $143.7698   $143.77   $143.75   $143.80  
  Purchase #5 $111.57   12.862%   $125.9201   $125.92   $125.90   $125.90  
  Purchase #6 $203.70   6.242%   $216.415   $216.42   $216.40   $216.40  
  Purchase #7 $163.57   3.805%   $169.7938   $169.79   $169.80   $169.80  
  7 purchase totals = $923.26       $1,002.9441   $1,002.94   $1,002.90   $1,003.00