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 $65.87   5.777%   $69.6753   $69.68   $69.70   $69.70  
  Purchase #2 $150.51   6.529%   $160.3368   $160.34   $160.35   $160.30  
  Purchase #3 $101.38   9.713%   $111.227   $111.23   $111.25   $111.20  
  Purchase #4 $39.59   4.571%   $41.3997   $41.40   $41.40   $41.40  
  Purchase #5 $83.48   3.702%   $86.5704   $86.57   $86.55   $86.60  
  Purchase #6 $91.42   3.138%   $94.2888   $94.29   $94.30   $94.30  
  Purchase #7 $211.78   7.411%   $227.475   $227.48   $227.50   $227.50  
  7 purchase totals = $744.03       $790.9730   $790.99   $791.05   $791.00