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 $80.89   5.707%   $85.5064   $85.51   $85.50   $85.50  
  Purchase #2 $202.57   13.119%   $229.1452   $229.15   $229.15   $229.10  
  Purchase #3 $248.49   11.789%   $277.7845   $277.78   $277.80   $277.80  
  Purchase #4 $87.73   8.363%   $95.0669   $95.07   $95.05   $95.10  
  Purchase #5 $43.42   12.552%   $48.8701   $48.87   $48.85   $48.90  
  Purchase #6 $47.99   9.129%   $52.371   $52.37   $52.35   $52.40  
  Purchase #7 $239.47   8.735%   $260.3877   $260.39   $260.40   $260.40  
  7 purchase totals = $950.56       $1,049.1318   $1,049.14   $1,049.10   $1,049.20