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 $187.67   7.601%   $201.9348   $201.93   $201.95   $201.90  
  Purchase #2 $250.29   13.405%   $283.8414   $283.84   $283.85   $283.80  
  Purchase #3 $233.84   10.686%   $258.8281   $258.83   $258.85   $258.80  
  Purchase #4 $141.61   8.161%   $153.1668   $153.17   $153.15   $153.20  
  Purchase #5 $34.96   9.144%   $38.1567   $38.16   $38.15   $38.20  
  Purchase #6 $58.54   13.206%   $66.2708   $66.27   $66.25   $66.30  
  Purchase #7 $117.53   11.470%   $131.0107   $131.01   $131.00   $131.00  
  7 purchase totals = $1,024.44       $1,133.2093   $1,133.21   $1,133.20   $1,133.20