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 $94.72   12.332%   $106.4009   $106.40   $106.40   $106.40  
  Purchase #2 $238.33   8.421%   $258.3998   $258.40   $258.40   $258.40  
  Purchase #3 $22.71   13.445%   $25.7634   $25.76   $25.75   $25.80  
  Purchase #4 $230.82   11.187%   $256.6418   $256.64   $256.65   $256.60  
  Purchase #5 $164.97   12.471%   $185.5434   $185.54   $185.55   $185.50  
  Purchase #6 $191.71   6.658%   $204.4741   $204.47   $204.45   $204.50  
  Purchase #7 $191.58   3.861%   $198.9769   $198.98   $199.00   $199.00  
  7 purchase totals = $1,134.84       $1,236.2003   $1,236.19   $1,236.20   $1,236.20