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 $185.52   6.458%   $197.5009   $197.50   $197.50   $197.50  
  Purchase #2 $38.56   10.474%   $42.5988   $42.60   $42.60   $42.60  
  Purchase #3 $30.43   7.302%   $32.652   $32.65   $32.65   $32.70  
  Purchase #4 $117.63   4.220%   $122.594   $122.59   $122.60   $122.60  
  Purchase #5 $11.82   5.558%   $12.477   $12.48   $12.50   $12.50  
  Purchase #6 $77.90   3.607%   $80.7099   $80.71   $80.70   $80.70  
  Purchase #7 $67.71   12.173%   $75.9523   $75.95   $75.95   $76.00  
  7 purchase totals = $529.57       $564.4849   $564.48   $564.50   $564.60