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 $124.62   13.251%   $141.1334   $141.13   $141.15   $141.10  
  Purchase #2 $179.31   10.110%   $197.4382   $197.44   $197.45   $197.40  
  Purchase #3 $239.74   12.393%   $269.451   $269.45   $269.45   $269.50  
  Purchase #4 $173.78   6.393%   $184.8898   $184.89   $184.90   $184.90  
  Purchase #5 $101.95   5.746%   $107.808   $107.81   $107.80   $107.80  
  Purchase #6 $40.36   6.474%   $42.9729   $42.97   $42.95   $43.00  
  Purchase #7 $51.48   3.140%   $53.0965   $53.10   $53.10   $53.10  
  7 purchase totals = $911.24       $996.7898   $996.79   $996.80   $996.80