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 $172.44   12.621%   $194.2037   $194.20   $194.20   $194.20  
  Purchase #2 $200.84   7.516%   $215.9351   $215.94   $215.95   $215.90  
  Purchase #3 $63.42   10.344%   $69.9802   $69.98   $70.00   $70.00  
  Purchase #4 $213.76   5.370%   $225.2389   $225.24   $225.25   $225.20  
  Purchase #5 $196.74   12.598%   $221.5253   $221.53   $221.55   $221.50  
  Purchase #6 $223.79   8.589%   $243.0113   $243.01   $243.00   $243.00  
  Purchase #7 $81.92   8.862%   $89.1798   $89.18   $89.20   $89.20  
  7 purchase totals = $1,152.91       $1,259.0743   $1,259.08   $1,259.15   $1,259.00