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 $230.87   11.760%   $258.0203   $258.02   $258.00   $258.00  
  Purchase #2 $163.81   6.194%   $173.9564   $173.96   $173.95   $174.00  
  Purchase #3 $149.98   6.807%   $160.1891   $160.19   $160.20   $160.20  
  Purchase #4 $113.74   8.289%   $123.1679   $123.17   $123.15   $123.20  
  Purchase #5 $68.46   5.541%   $72.2534   $72.25   $72.25   $72.30  
  Purchase #6 $181.86   6.436%   $193.5645   $193.56   $193.55   $193.60  
  Purchase #7 $42.66   3.835%   $44.296   $44.30   $44.30   $44.30  
  7 purchase totals = $951.38       $1,025.4476   $1,025.45   $1,025.40   $1,025.60