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 $54.75   10.112%   $60.2863   $60.29   $60.30   $60.30  
  Purchase #2 $179.73   6.185%   $190.8463   $190.85   $190.85   $190.80  
  Purchase #3 $16.62   6.631%   $17.7221   $17.72   $17.70   $17.70  
  Purchase #4 $226.92   12.690%   $255.7161   $255.72   $255.70   $255.70  
  Purchase #5 $169.85   8.462%   $184.2227   $184.22   $184.20   $184.20  
  Purchase #6 $160.63   3.540%   $166.3163   $166.32   $166.30   $166.30  
  Purchase #7 $119.41   7.821%   $128.7491   $128.75   $128.75   $128.70  
  7 purchase totals = $927.91       $1,003.8589   $1,003.87   $1,003.80   $1,003.70