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 $61.86   8.361%   $67.0321   $67.03   $67.05   $67.00  
  Purchase #2 $213.88   5.604%   $225.8658   $225.87   $225.85   $225.90  
  Purchase #3 $221.36   3.656%   $229.4529   $229.45   $229.45   $229.50  
  Purchase #4 $180.86   3.539%   $187.2606   $187.26   $187.25   $187.30  
  Purchase #5 $197.52   5.742%   $208.8616   $208.86   $208.85   $208.90  
  Purchase #6 $94.94   8.155%   $102.6824   $102.68   $102.70   $102.70  
  Purchase #7 $106.64   13.620%   $121.1644   $121.16   $121.15   $121.20  
  7 purchase totals = $1,077.06       $1,142.3198   $1,142.31   $1,142.30   $1,142.50