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 $24.42   8.260%   $26.4371   $26.44   $26.45   $26.40  
  Purchase #2 $219.95   12.337%   $247.0852   $247.09   $247.10   $247.10  
  Purchase #3 $24.60   13.762%   $27.9855   $27.99   $28.00   $28.00  
  Purchase #4 $244.27   3.776%   $253.4936   $253.49   $253.50   $253.50  
  Purchase #5 $189.73   3.290%   $195.9721   $195.97   $195.95   $196.00  
  Purchase #6 $172.66   4.633%   $180.6593   $180.66   $180.65   $180.70  
  Purchase #7 $125.63   7.811%   $135.443   $135.44   $135.45   $135.40  
  7 purchase totals = $1,001.26       $1,067.0758   $1,067.08   $1,067.10   $1,067.10