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 $18.34   9.718%   $20.1223   $20.12   $20.10   $20.10  
  Purchase #2 $96.84   10.647%   $107.1506   $107.15   $107.15   $107.20  
  Purchase #3 $35.69   6.467%   $37.9981   $38.00   $38.00   $38.00  
  Purchase #4 $66.37   5.437%   $69.9785   $69.98   $70.00   $70.00  
  Purchase #5 $41.41   12.737%   $46.6844   $46.68   $46.70   $46.70  
  Purchase #6 $113.93   5.206%   $119.8612   $119.86   $119.85   $119.90  
  Purchase #7 $194.30   10.561%   $214.82   $214.82   $214.80   $214.80  
  7 purchase totals = $566.88       $616.6151   $616.61   $616.60   $616.70