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 $235.37   12.151%   $263.9698   $263.97   $263.95   $264.00  
  Purchase #2 $186.78   8.119%   $201.9447   $201.94   $201.95   $201.90  
  Purchase #3 $28.87   9.123%   $31.5038   $31.50   $31.50   $31.50  
  Purchase #4 $213.86   7.504%   $229.9081   $229.91   $229.90   $229.90  
  Purchase #5 $124.84   10.375%   $137.7922   $137.79   $137.80   $137.80  
  Purchase #6 $164.72   13.376%   $186.7529   $186.75   $186.75   $186.80  
  Purchase #7 $147.42   5.456%   $155.4632   $155.46   $155.45   $155.50  
  7 purchase totals = $1,101.86       $1,207.3347   $1,207.32   $1,207.30   $1,207.40