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 $169.60   13.193%   $191.9753   $191.98   $192.00   $192.00  
  Purchase #2 $127.39   12.557%   $143.3864   $143.39   $143.40   $143.40  
  Purchase #3 $179.35   3.431%   $185.5035   $185.50   $185.50   $185.50  
  Purchase #4 $213.99   8.642%   $232.483   $232.48   $232.50   $232.50  
  Purchase #5 $222.60   8.699%   $241.964   $241.96   $241.95   $242.00  
  Purchase #6 $184.90   5.111%   $194.3502   $194.35   $194.35   $194.40  
  Purchase #7 $226.38   8.409%   $245.4163   $245.42   $245.40   $245.40  
  7 purchase totals = $1,324.21       $1,435.0787   $1,435.08   $1,435.10   $1,435.20