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 $147.47   3.254%   $152.2687   $152.27   $152.25   $152.30  
  Purchase #2 $95.97   5.705%   $101.4451   $101.45   $101.45   $101.40  
  Purchase #3 $209.81   9.381%   $229.4923   $229.49   $229.50   $229.50  
  Purchase #4 $136.77   5.504%   $144.2978   $144.30   $144.30   $144.30  
  Purchase #5 $45.42   11.625%   $50.7001   $50.70   $50.70   $50.70  
  Purchase #6 $197.92   6.666%   $211.1133   $211.11   $211.10   $211.10  
  Purchase #7 $154.69   5.655%   $163.4377   $163.44   $163.45   $163.40  
  7 purchase totals = $988.05       $1,052.7550   $1,052.76   $1,052.75   $1,052.70