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 $98.33   3.614%   $101.8836   $101.88   $101.90   $101.90  
  Purchase #2 $181.74   11.421%   $202.4965   $202.50   $202.50   $202.50  
  Purchase #3 $82.41   11.635%   $91.9984   $92.00   $92.00   $92.00  
  Purchase #4 $67.26   10.868%   $74.5698   $74.57   $74.55   $74.60  
  Purchase #5 $179.64   8.400%   $194.7298   $194.73   $194.75   $194.70  
  Purchase #6 $139.64   6.688%   $148.9791   $148.98   $149.00   $149.00  
  Purchase #7 $221.92   5.795%   $234.7803   $234.78   $234.80   $234.80  
  7 purchase totals = $970.94       $1,049.4375   $1,049.44   $1,049.50   $1,049.50