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 $130.77   12.333%   $146.8979   $146.90   $146.90   $146.90  
  Purchase #2 $173.97   12.623%   $195.9302   $195.93   $195.95   $195.90  
  Purchase #3 $234.74   5.863%   $248.5028   $248.50   $248.50   $248.50  
  Purchase #4 $213.96   13.303%   $242.4231   $242.42   $242.40   $242.40  
  Purchase #5 $135.73   3.870%   $140.9828   $140.98   $141.00   $141.00  
  Purchase #6 $177.92   8.783%   $193.5467   $193.55   $193.55   $193.50  
  Purchase #7 $197.93   7.201%   $212.1829   $212.18   $212.20   $212.20  
  7 purchase totals = $1,265.02       $1,380.4664   $1,380.46   $1,380.50   $1,380.40