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 $83.89   11.123%   $93.2211   $93.22   $93.20   $93.20  
  Purchase #2 $87.25   8.442%   $94.6156   $94.62   $94.60   $94.60  
  Purchase #3 $11.37   6.706%   $12.1325   $12.13   $12.15   $12.10  
  Purchase #4 $156.72   5.243%   $164.9368   $164.94   $164.95   $164.90  
  Purchase #5 $130.74   11.289%   $145.4992   $145.50   $145.50   $145.50  
  Purchase #6 $96.27   10.160%   $106.051   $106.05   $106.05   $106.10  
  Purchase #7 $233.30   13.387%   $264.5319   $264.53   $264.55   $264.50  
  7 purchase totals = $799.54       $880.9881   $880.99   $881.00   $880.90