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 $61.84   8.474%   $67.0803   $67.08   $67.10   $67.10  
  Purchase #2 $187.76   4.750%   $196.6786   $196.68   $196.70   $196.70  
  Purchase #3 $37.98   4.869%   $39.8292   $39.83   $39.85   $39.80  
  Purchase #4 $141.50   10.665%   $156.591   $156.59   $156.60   $156.60  
  Purchase #5 $20.48   11.369%   $22.8084   $22.81   $22.80   $22.80  
  Purchase #6 $135.70   11.412%   $151.1861   $151.19   $151.20   $151.20  
  Purchase #7 $206.36   12.318%   $231.7794   $231.78   $231.80   $231.80  
  7 purchase totals = $791.62       $865.9530   $865.96   $866.05   $866.00