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 $95.40   6.762%   $101.8509   $101.85   $101.85   $101.90  
  Purchase #2 $20.93   7.661%   $22.5334   $22.53   $22.55   $22.50  
  Purchase #3 $238.54   7.380%   $256.1443   $256.14   $256.15   $256.10  
  Purchase #4 $39.62   12.566%   $44.5986   $44.60   $44.60   $44.60  
  Purchase #5 $99.31   9.583%   $108.8269   $108.83   $108.85   $108.80  
  Purchase #6 $70.32   7.310%   $75.4604   $75.46   $75.45   $75.50  
  Purchase #7 $181.72   6.805%   $194.086   $194.09   $194.10   $194.10  
  7 purchase totals = $745.84       $803.5005   $803.50   $803.55   $803.50