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 $187.39   8.706%   $203.7042   $203.70   $203.70   $203.70  
  Purchase #2 $26.30   4.115%   $27.3822   $27.38   $27.40   $27.40  
  Purchase #3 $45.87   10.738%   $50.7955   $50.80   $50.80   $50.80  
  Purchase #4 $175.79   5.436%   $185.3459   $185.35   $185.35   $185.30  
  Purchase #5 $130.86   13.379%   $148.3678   $148.37   $148.35   $148.40  
  Purchase #6 $202.49   3.598%   $209.7756   $209.78   $209.80   $209.80  
  Purchase #7 $245.44   13.216%   $277.8774   $277.88   $277.90   $277.90  
  7 purchase totals = $1,014.14       $1,103.2486   $1,103.26   $1,103.30   $1,103.30