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 $32.84   10.203%   $36.1907   $36.19   $36.20   $36.20  
  Purchase #2 $141.27   13.802%   $160.7681   $160.77   $160.75   $160.80  
  Purchase #3 $159.95   11.490%   $178.3283   $178.33   $178.35   $178.30  
  Purchase #4 $188.81   9.635%   $207.0018   $207.00   $207.00   $207.00  
  Purchase #5 $125.58   4.755%   $131.5513   $131.55   $131.55   $131.60  
  Purchase #6 $76.81   10.192%   $84.6385   $84.64   $84.65   $84.60  
  Purchase #7 $195.92   11.547%   $218.5429   $218.54   $218.55   $218.50  
  7 purchase totals = $921.18       $1,017.0216   $1,017.02   $1,017.05   $1,017.00