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 $226.87   8.532%   $246.2265   $246.23   $246.25   $246.20  
  Purchase #2 $161.67   6.122%   $171.5674   $171.57   $171.55   $171.60  
  Purchase #3 $38.98   5.427%   $41.0954   $41.10   $41.10   $41.10  
  Purchase #4 $218.63   12.350%   $245.6308   $245.63   $245.65   $245.60  
  Purchase #5 $127.36   6.163%   $135.2092   $135.21   $135.20   $135.20  
  Purchase #6 $76.37   13.151%   $86.4134   $86.41   $86.40   $86.40  
  Purchase #7 $185.85   10.183%   $204.7751   $204.78   $204.80   $204.80  
  7 purchase totals = $1,035.73       $1,130.9178   $1,130.93   $1,130.95   $1,130.90