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 $189.48   8.223%   $205.0609   $205.06   $205.05   $205.10  
  Purchase #2 $95.37   12.246%   $107.049   $107.05   $107.05   $107.00  
  Purchase #3 $6.95   9.300%   $7.5964   $7.60   $7.60   $7.60  
  Purchase #4 $191.67   6.423%   $203.981   $203.98   $204.00   $204.00  
  Purchase #5 $20.98   9.768%   $23.0293   $23.03   $23.05   $23.00  
  Purchase #6 $109.89   3.573%   $113.8164   $113.82   $113.80   $113.80  
  Purchase #7 $55.55   13.177%   $62.8698   $62.87   $62.85   $62.90  
  7 purchase totals = $669.89       $723.4028   $723.41   $723.40   $723.40