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 $122.69   6.137%   $130.2195   $130.22   $130.20   $130.20  
  Purchase #2 $242.93   5.236%   $255.6498   $255.65   $255.65   $255.60  
  Purchase #3 $217.51   6.672%   $232.0223   $232.02   $232.00   $232.00  
  Purchase #4 $72.51   6.568%   $77.2725   $77.27   $77.25   $77.30  
  Purchase #5 $202.66   13.787%   $230.6007   $230.60   $230.60   $230.60  
  Purchase #6 $64.60   12.414%   $72.6194   $72.62   $72.60   $72.60  
  Purchase #7 $127.34   5.483%   $134.3221   $134.32   $134.30   $134.30  
  7 purchase totals = $1,050.24       $1,132.7063   $1,132.70   $1,132.60   $1,132.60