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 $64.91   6.254%   $68.9695   $68.97   $68.95   $69.00  
  Purchase #2 $44.42   5.304%   $46.776   $46.78   $46.80   $46.80  
  Purchase #3 $56.86   10.458%   $62.8064   $62.81   $62.80   $62.80  
  Purchase #4 $123.74   7.861%   $133.4672   $133.47   $133.45   $133.50  
  Purchase #5 $211.49   10.185%   $233.0303   $233.03   $233.05   $233.00  
  Purchase #6 $60.40   6.340%   $64.2294   $64.23   $64.25   $64.20  
  Purchase #7 $188.52   4.359%   $196.7376   $196.74   $196.75   $196.70  
  7 purchase totals = $750.34       $806.0164   $806.03   $806.05   $806.00