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 $183.52   3.829%   $190.547   $190.55   $190.55   $190.50  
  Purchase #2 $31.87   8.661%   $34.6303   $34.63   $34.65   $34.60  
  Purchase #3 $43.52   4.372%   $45.4227   $45.42   $45.40   $45.40  
  Purchase #4 $61.94   9.225%   $67.654   $67.65   $67.65   $67.70  
  Purchase #5 $174.53   8.121%   $188.7036   $188.70   $188.70   $188.70  
  Purchase #6 $246.74   9.138%   $269.2871   $269.29   $269.30   $269.30  
  Purchase #7 $76.99   7.701%   $82.919   $82.92   $82.90   $82.90  
  7 purchase totals = $819.11       $879.1637   $879.16   $879.15   $879.10