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 $50.98   3.204%   $52.6134   $52.61   $52.60   $52.60  
  Purchase #2 $25.94   5.646%   $27.4046   $27.40   $27.40   $27.40  
  Purchase #3 $249.60   7.480%   $268.2701   $268.27   $268.25   $268.30  
  Purchase #4 $161.29   3.822%   $167.4545   $167.45   $167.45   $167.50  
  Purchase #5 $53.77   5.357%   $56.6505   $56.65   $56.65   $56.70  
  Purchase #6 $109.46   11.731%   $122.3008   $122.30   $122.30   $122.30  
  Purchase #7 $39.94   11.642%   $44.5898   $44.59   $44.60   $44.60  
  7 purchase totals = $690.98       $739.2837   $739.27   $739.25   $739.40