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 $75.63   9.762%   $83.013   $83.01   $83.00   $83.00  
  Purchase #2 $189.70   6.239%   $201.5354   $201.54   $201.55   $201.50  
  Purchase #3 $70.55   10.479%   $77.9429   $77.94   $77.95   $77.90  
  Purchase #4 $113.35   12.507%   $127.5267   $127.53   $127.55   $127.50  
  Purchase #5 $72.54   3.509%   $75.0854   $75.09   $75.10   $75.10  
  Purchase #6 $216.59   8.456%   $234.9049   $234.90   $234.90   $234.90  
  Purchase #7 $232.64   6.377%   $247.4755   $247.48   $247.50   $247.50  
  7 purchase totals = $971.00       $1,047.4838   $1,047.49   $1,047.55   $1,047.40