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 $204.76   13.634%   $232.677   $232.68   $232.70   $232.70  
  Purchase #2 $90.48   6.344%   $96.2201   $96.22   $96.20   $96.20  
  Purchase #3 $230.44   6.656%   $245.7781   $245.78   $245.80   $245.80  
  Purchase #4 $48.50   4.406%   $50.6369   $50.64   $50.65   $50.60  
  Purchase #5 $164.36   6.372%   $174.833   $174.83   $174.85   $174.80  
  Purchase #6 $19.96   7.532%   $21.4634   $21.46   $21.45   $21.50  
  Purchase #7 $204.46   12.158%   $229.3182   $229.32   $229.30   $229.30  
  7 purchase totals = $962.96       $1,050.9267   $1,050.93   $1,050.95   $1,050.90