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 $55.81   10.674%   $61.7672   $61.77   $61.75   $61.80  
  Purchase #2 $209.28   8.279%   $226.6063   $226.61   $226.60   $226.60  
  Purchase #3 $131.98   7.755%   $142.215   $142.22   $142.20   $142.20  
  Purchase #4 $9.71   3.120%   $10.013   $10.01   $10.00   $10.00  
  Purchase #5 $187.94   9.351%   $205.5143   $205.51   $205.50   $205.50  
  Purchase #6 $181.38   12.180%   $203.4721   $203.47   $203.45   $203.50  
  Purchase #7 $201.72   11.340%   $224.595   $224.60   $224.60   $224.60  
  7 purchase totals = $977.82       $1,074.1829   $1,074.19   $1,074.10   $1,074.20