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 $101.43   4.694%   $106.1911   $106.19   $106.20   $106.20  
  Purchase #2 $62.61   13.241%   $70.9002   $70.90   $70.90   $70.90  
  Purchase #3 $67.45   12.658%   $75.9878   $75.99   $76.00   $76.00  
  Purchase #4 $156.68   10.160%   $172.5987   $172.60   $172.60   $172.60  
  Purchase #5 $102.95   12.610%   $115.932   $115.93   $115.95   $115.90  
  Purchase #6 $171.27   3.176%   $176.7095   $176.71   $176.70   $176.70  
  Purchase #7 $162.29   11.513%   $180.9744   $180.97   $180.95   $181.00  
  7 purchase totals = $824.68       $899.2937   $899.29   $899.30   $899.30