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 $88.73   6.538%   $94.5312   $94.53   $94.55   $94.50  
  Purchase #2 $232.71   3.774%   $241.4925   $241.49   $241.50   $241.50  
  Purchase #3 $229.52   5.859%   $242.9676   $242.97   $242.95   $243.00  
  Purchase #4 $35.71   6.301%   $37.9601   $37.96   $37.95   $38.00  
  Purchase #5 $123.70   13.591%   $140.5121   $140.51   $140.50   $140.50  
  Purchase #6 $98.83   3.458%   $102.2475   $102.25   $102.25   $102.20  
  Purchase #7 $218.27   5.414%   $230.0871   $230.09   $230.10   $230.10  
  7 purchase totals = $1,027.47       $1,089.7981   $1,089.80   $1,089.80   $1,089.80