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 $33.26   8.420%   $36.0605   $36.06   $36.05   $36.10  
  Purchase #2 $116.95   7.595%   $125.8324   $125.83   $125.85   $125.80  
  Purchase #3 $121.40   5.323%   $127.8621   $127.86   $127.85   $127.90  
  Purchase #4 $36.72   6.109%   $38.9632   $38.96   $38.95   $39.00  
  Purchase #5 $95.87   6.484%   $102.0862   $102.09   $102.10   $102.10  
  Purchase #6 $166.63   12.444%   $187.3654   $187.37   $187.35   $187.40  
  Purchase #7 $132.38   9.282%   $144.6675   $144.67   $144.65   $144.70  
  7 purchase totals = $703.21       $762.8373   $762.84   $762.80   $763.00