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 $82.49   3.264%   $85.1825   $85.18   $85.20   $85.20  
  Purchase #2 $111.72   3.755%   $115.9151   $115.92   $115.90   $115.90  
  Purchase #3 $32.92   6.254%   $34.9788   $34.98   $35.00   $35.00  
  Purchase #4 $246.55   3.471%   $255.1078   $255.11   $255.10   $255.10  
  Purchase #5 $88.66   11.769%   $99.0944   $99.09   $99.10   $99.10  
  Purchase #6 $43.82   8.632%   $47.6025   $47.60   $47.60   $47.60  
  Purchase #7 $167.75   4.856%   $175.8959   $175.90   $175.90   $175.90  
  7 purchase totals = $773.91       $813.7770   $813.78   $813.80   $813.80