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 $131.27   8.596%   $142.554   $142.55   $142.55   $142.60  
  Purchase #2 $74.72   13.511%   $84.8154   $84.82   $84.80   $84.80  
  Purchase #3 $87.49   8.804%   $95.1926   $95.19   $95.20   $95.20  
  Purchase #4 $177.30   4.348%   $185.009   $185.01   $185.00   $185.00  
  Purchase #5 $121.28   4.188%   $126.3592   $126.36   $126.35   $126.40  
  Purchase #6 $154.61   8.565%   $167.8523   $167.85   $167.85   $167.90  
  Purchase #7 $214.93   3.259%   $221.9346   $221.93   $221.95   $221.90  
  7 purchase totals = $961.60       $1,023.7171   $1,023.71   $1,023.70   $1,023.80