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 $152.78   4.748%   $160.034   $160.03   $160.05   $160.00  
  Purchase #2 $249.32   11.417%   $277.7849   $277.78   $277.80   $277.80  
  Purchase #3 $73.55   4.734%   $77.0319   $77.03   $77.05   $77.00  
  Purchase #4 $36.62   5.325%   $38.57   $38.57   $38.55   $38.60  
  Purchase #5 $167.62   3.645%   $173.7297   $173.73   $173.75   $173.70  
  Purchase #6 $86.53   6.405%   $92.0722   $92.07   $92.05   $92.10  
  Purchase #7 $64.67   4.772%   $67.7561   $67.76   $67.75   $67.80  
  7 purchase totals = $831.09       $886.9788   $886.97   $887.00   $887.00