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 $224.73   3.565%   $232.7416   $232.74   $232.75   $232.70  
  Purchase #2 $213.62   13.659%   $242.7984   $242.80   $242.80   $242.80  
  Purchase #3 $68.58   11.358%   $76.3693   $76.37   $76.35   $76.40  
  Purchase #4 $175.35   4.468%   $183.1846   $183.18   $183.20   $183.20  
  Purchase #5 $198.57   3.496%   $205.512   $205.51   $205.50   $205.50  
  Purchase #6 $35.75   11.809%   $39.9717   $39.97   $39.95   $40.00  
  Purchase #7 $166.93   7.698%   $179.7803   $179.78   $179.80   $179.80  
  7 purchase totals = $1,083.53       $1,160.3579   $1,160.35   $1,160.35   $1,160.40