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 $68.47   3.332%   $70.7514   $70.75   $70.75   $70.80  
  Purchase #2 $198.25   5.694%   $209.5384   $209.54   $209.55   $209.50  
  Purchase #3 $61.94   10.737%   $68.5905   $68.59   $68.60   $68.60  
  Purchase #4 $174.96   13.136%   $197.9427   $197.94   $197.95   $197.90  
  Purchase #5 $72.64   7.300%   $77.9427   $77.94   $77.95   $77.90  
  Purchase #6 $97.59   9.147%   $106.5166   $106.52   $106.50   $106.50  
  Purchase #7 $140.52   11.686%   $156.9412   $156.94   $156.95   $156.90  
  7 purchase totals = $814.37       $888.2235   $888.22   $888.25   $888.10