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 $84.43   10.713%   $93.475   $93.48   $93.50   $93.50  
  Purchase #2 $186.94   13.614%   $212.39   $212.39   $212.40   $212.40  
  Purchase #3 $235.59   4.287%   $245.6897   $245.69   $245.70   $245.70  
  Purchase #4 $245.71   3.693%   $254.7841   $254.78   $254.80   $254.80  
  Purchase #5 $192.87   11.158%   $214.3904   $214.39   $214.40   $214.40  
  Purchase #6 $147.35   5.829%   $155.939   $155.94   $155.95   $155.90  
  Purchase #7 $231.71   9.418%   $253.5324   $253.53   $253.55   $253.50  
  7 purchase totals = $1,324.60       $1,430.2006   $1,430.20   $1,430.30   $1,430.20