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 $215.56   6.348%   $229.2437   $229.24   $229.25   $229.20  
  Purchase #2 $192.46   6.286%   $204.558   $204.56   $204.55   $204.60  
  Purchase #3 $100.69   4.493%   $105.214   $105.21   $105.20   $105.20  
  Purchase #4 $239.91   5.335%   $252.7092   $252.71   $252.70   $252.70  
  Purchase #5 $131.57   3.108%   $135.6592   $135.66   $135.65   $135.70  
  Purchase #6 $53.98   13.637%   $61.3413   $61.34   $61.35   $61.30  
  Purchase #7 $58.88   4.457%   $61.5043   $61.50   $61.50   $61.50  
  7 purchase totals = $993.05       $1,050.2297   $1,050.22   $1,050.20   $1,050.20