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 $189.62   8.270%   $205.3016   $205.30   $205.30   $205.30  
  Purchase #2 $247.31   8.686%   $268.7913   $268.79   $268.80   $268.80  
  Purchase #3 $132.71   12.750%   $149.6305   $149.63   $149.65   $149.60  
  Purchase #4 $60.30   9.128%   $65.8042   $65.80   $65.80   $65.80  
  Purchase #5 $191.81   13.216%   $217.1596   $217.16   $217.15   $217.20  
  Purchase #6 $114.59   5.339%   $120.708   $120.71   $120.70   $120.70  
  Purchase #7 $50.43   6.306%   $53.6101   $53.61   $53.60   $53.60  
  7 purchase totals = $986.77       $1,081.0053   $1,081.00   $1,081.00   $1,081.00