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 $44.43   12.490%   $49.9793   $49.98   $50.00   $50.00  
  Purchase #2 $170.91   12.643%   $192.5182   $192.52   $192.50   $192.50  
  Purchase #3 $20.72   12.433%   $23.2961   $23.30   $23.30   $23.30  
  Purchase #4 $82.27   6.373%   $87.5131   $87.51   $87.50   $87.50  
  Purchase #5 $229.71   6.173%   $243.89   $243.89   $243.90   $243.90  
  Purchase #6 $9.45   5.802%   $9.9983   $10.00   $10.00   $10.00  
  Purchase #7 $139.60   4.108%   $145.3348   $145.33   $145.35   $145.30  
  7 purchase totals = $697.09       $752.5298   $752.53   $752.55   $752.50