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 $75.52   5.400%   $79.5981   $79.60   $79.60   $79.60  
  Purchase #2 $37.50   6.753%   $40.0324   $40.03   $40.05   $40.00  
  Purchase #3 $185.33   12.671%   $208.8132   $208.81   $208.80   $208.80  
  Purchase #4 $124.38   3.148%   $128.2955   $128.30   $128.30   $128.30  
  Purchase #5 $158.55   8.595%   $172.1774   $172.18   $172.20   $172.20  
  Purchase #6 $32.33   4.364%   $33.7409   $33.74   $33.75   $33.70  
  Purchase #7 $89.60   12.869%   $101.1306   $101.13   $101.15   $101.10  
  7 purchase totals = $703.21       $763.7881   $763.79   $763.85   $763.70