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 $87.69   5.750%   $92.7322   $92.73   $92.75   $92.70  
  Purchase #2 $246.70   10.540%   $272.7022   $272.70   $272.70   $272.70  
  Purchase #3 $60.69   7.166%   $65.039   $65.04   $65.05   $65.00  
  Purchase #4 $187.29   10.604%   $207.1502   $207.15   $207.15   $207.20  
  Purchase #5 $155.80   5.199%   $163.9   $163.90   $163.90   $163.90  
  Purchase #6 $239.86   9.306%   $262.1814   $262.18   $262.20   $262.20  
  Purchase #7 $182.80   5.405%   $192.6803   $192.68   $192.70   $192.70  
  7 purchase totals = $1,160.83       $1,256.3853   $1,256.38   $1,256.45   $1,256.40