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 $132.54   8.704%   $144.0763   $144.08   $144.10   $144.10  
  Purchase #2 $90.40   5.765%   $95.6116   $95.61   $95.60   $95.60  
  Purchase #3 $243.52   5.826%   $257.7075   $257.71   $257.70   $257.70  
  Purchase #4 $37.92   7.226%   $40.6601   $40.66   $40.65   $40.70  
  Purchase #5 $53.61   4.687%   $56.1227   $56.12   $56.10   $56.10  
  Purchase #6 $196.47   3.162%   $202.6824   $202.68   $202.70   $202.70  
  Purchase #7 $218.50   4.214%   $227.7076   $227.71   $227.70   $227.70  
  7 purchase totals = $972.96       $1,024.5682   $1,024.57   $1,024.55   $1,024.60