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 $70.86   4.798%   $74.2599   $74.26   $74.25   $74.30  
  Purchase #2 $202.92   13.305%   $229.9185   $229.92   $229.90   $229.90  
  Purchase #3 $146.67   13.675%   $166.7271   $166.73   $166.75   $166.70  
  Purchase #4 $195.52   13.679%   $222.2652   $222.27   $222.25   $222.30  
  Purchase #5 $38.46   12.311%   $43.1948   $43.19   $43.20   $43.20  
  Purchase #6 $11.39   12.779%   $12.8455   $12.85   $12.85   $12.80  
  Purchase #7 $223.74   10.799%   $247.9017   $247.90   $247.90   $247.90  
  7 purchase totals = $889.56       $997.1127   $997.12   $997.10   $997.10