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 $71.42   6.379%   $75.9759   $75.98   $76.00   $76.00  
  Purchase #2 $206.25   11.863%   $230.7174   $230.72   $230.70   $230.70  
  Purchase #3 $172.98   10.551%   $191.2311   $191.23   $191.25   $191.20  
  Purchase #4 $47.47   4.620%   $49.6631   $49.66   $49.65   $49.70  
  Purchase #5 $189.91   3.213%   $196.0118   $196.01   $196.00   $196.00  
  Purchase #6 $204.44   12.750%   $230.5061   $230.51   $230.50   $230.50  
  Purchase #7 $245.76   13.421%   $278.7434   $278.74   $278.75   $278.70  
  7 purchase totals = $1,138.23       $1,252.8488   $1,252.85   $1,252.85   $1,252.80