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 $62.72   5.820%   $66.3703   $66.37   $66.35   $66.40  
  Purchase #2 $190.36   4.722%   $199.3488   $199.35   $199.35   $199.30  
  Purchase #3 $41.49   3.583%   $42.9766   $42.98   $43.00   $43.00  
  Purchase #4 $76.47   5.738%   $80.8578   $80.86   $80.85   $80.90  
  Purchase #5 $24.74   11.233%   $27.519   $27.52   $27.50   $27.50  
  Purchase #6 $45.79   5.558%   $48.335   $48.34   $48.35   $48.30  
  Purchase #7 $58.42   12.736%   $65.8604   $65.86   $65.85   $65.90  
  7 purchase totals = $499.99       $531.2679   $531.28   $531.25   $531.30