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 $92.30   6.859%   $98.6309   $98.63   $98.65   $98.60  
  Purchase #2 $156.32   10.607%   $172.9009   $172.90   $172.90   $172.90  
  Purchase #3 $223.72   5.386%   $235.7696   $235.77   $235.75   $235.80  
  Purchase #4 $179.30   4.343%   $187.087   $187.09   $187.10   $187.10  
  Purchase #5 $36.94   13.623%   $41.9723   $41.97   $41.95   $42.00  
  Purchase #6 $70.52   4.586%   $73.754   $73.75   $73.75   $73.80  
  Purchase #7 $234.65   8.780%   $255.2523   $255.25   $255.25   $255.30  
  7 purchase totals = $993.75       $1,065.3670   $1,065.36   $1,065.35   $1,065.50