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 $65.58   12.493%   $73.7729   $73.77   $73.75   $73.80  
  Purchase #2 $158.34   11.392%   $176.3781   $176.38   $176.40   $176.40  
  Purchase #3 $14.81   11.375%   $16.4946   $16.49   $16.50   $16.50  
  Purchase #4 $225.90   8.492%   $245.0834   $245.08   $245.10   $245.10  
  Purchase #5 $172.27   10.247%   $189.9225   $189.92   $189.90   $189.90  
  Purchase #6 $184.87   13.216%   $209.3024   $209.30   $209.30   $209.30  
  Purchase #7 $234.56   13.820%   $266.9762   $266.98   $267.00   $267.00  
  7 purchase totals = $1,056.33       $1,177.9301   $1,177.92   $1,177.95   $1,178.00