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 $177.32   8.409%   $192.2308   $192.23   $192.25   $192.20  
  Purchase #2 $57.38   9.740%   $62.9688   $62.97   $62.95   $63.00  
  Purchase #3 $67.73   8.590%   $73.548   $73.55   $73.55   $73.50  
  Purchase #4 $31.84   3.388%   $32.9187   $32.92   $32.90   $32.90  
  Purchase #5 $242.35   11.814%   $270.9812   $270.98   $271.00   $271.00  
  Purchase #6 $246.58   12.731%   $277.9721   $277.97   $277.95   $278.00  
  Purchase #7 $164.91   11.543%   $183.9456   $183.95   $183.95   $183.90  
  7 purchase totals = $988.11       $1,094.5652   $1,094.57   $1,094.55   $1,094.50