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 $94.81   3.293%   $97.9321   $97.93   $97.95   $97.90  
  Purchase #2 $45.89   13.217%   $51.9553   $51.96   $51.95   $52.00  
  Purchase #3 $56.53   13.591%   $64.213   $64.21   $64.20   $64.20  
  Purchase #4 $117.64   13.671%   $133.7226   $133.72   $133.70   $133.70  
  Purchase #5 $167.51   11.411%   $186.6246   $186.62   $186.60   $186.60  
  Purchase #6 $239.46   5.249%   $252.0293   $252.03   $252.05   $252.00  
  Purchase #7 $232.32   8.503%   $252.0742   $252.07   $252.05   $252.10  
  7 purchase totals = $954.16       $1,038.5511   $1,038.54   $1,038.50   $1,038.50