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 $72.43   10.791%   $80.2459   $80.25   $80.25   $80.20  
  Purchase #2 $212.91   12.481%   $239.4833   $239.48   $239.50   $239.50  
  Purchase #3 $194.80   5.194%   $204.9179   $204.92   $204.90   $204.90  
  Purchase #4 $71.41   7.816%   $76.9914   $76.99   $77.00   $77.00  
  Purchase #5 $102.93   4.339%   $107.3961   $107.40   $107.40   $107.40  
  Purchase #6 $211.53   10.408%   $233.546   $233.55   $233.55   $233.50  
  Purchase #7 $245.30   3.804%   $254.6312   $254.63   $254.65   $254.60  
  7 purchase totals = $1,111.31       $1,197.2118   $1,197.22   $1,197.25   $1,197.10