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 $32.45   3.380%   $33.5468   $33.55   $33.55   $33.50  
  Purchase #2 $202.92   7.787%   $218.7214   $218.72   $218.70   $218.70  
  Purchase #3 $76.30   7.257%   $81.8371   $81.84   $81.85   $81.80  
  Purchase #4 $76.91   4.359%   $80.2625   $80.26   $80.25   $80.30  
  Purchase #5 $139.41   9.672%   $152.8937   $152.89   $152.90   $152.90  
  Purchase #6 $202.42   3.254%   $209.0067   $209.01   $209.00   $209.00  
  Purchase #7 $150.77   9.256%   $164.7253   $164.73   $164.75   $164.70  
  7 purchase totals = $881.18       $940.9935   $941.00   $941.00   $940.90