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 $194.60   5.568%   $205.4353   $205.44   $205.45   $205.40  
  Purchase #2 $231.92   11.204%   $257.9043   $257.90   $257.90   $257.90  
  Purchase #3 $212.78   8.551%   $230.9748   $230.97   $230.95   $231.00  
  Purchase #4 $148.28   13.519%   $168.326   $168.33   $168.35   $168.30  
  Purchase #5 $226.99   10.762%   $251.4187   $251.42   $251.40   $251.40  
  Purchase #6 $76.70   5.730%   $81.0949   $81.09   $81.10   $81.10  
  Purchase #7 $61.42   12.817%   $69.2922   $69.29   $69.30   $69.30  
  7 purchase totals = $1,152.69       $1,264.4462   $1,264.44   $1,264.45   $1,264.40