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 $122.47   10.110%   $134.8517   $134.85   $134.85   $134.90  
  Purchase #2 $132.62   6.847%   $141.7005   $141.70   $141.70   $141.70  
  Purchase #3 $41.81   13.867%   $47.6078   $47.61   $47.60   $47.60  
  Purchase #4 $186.67   11.727%   $208.5608   $208.56   $208.55   $208.60  
  Purchase #5 $165.95   4.179%   $172.8851   $172.89   $172.90   $172.90  
  Purchase #6 $244.29   3.570%   $253.0112   $253.01   $253.00   $253.00  
  Purchase #7 $113.89   6.220%   $120.974   $120.97   $120.95   $121.00  
  7 purchase totals = $1,007.70       $1,079.5911   $1,079.59   $1,079.55   $1,079.70