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 $97.84   8.283%   $105.9441   $105.94   $105.95   $105.90  
  Purchase #2 $249.90   13.425%   $283.4491   $283.45   $283.45   $283.40  
  Purchase #3 $62.49   10.366%   $68.9677   $68.97   $68.95   $69.00  
  Purchase #4 $70.33   10.169%   $77.4819   $77.48   $77.50   $77.50  
  Purchase #5 $36.98   6.725%   $39.4669   $39.47   $39.45   $39.50  
  Purchase #6 $246.42   4.140%   $256.6218   $256.62   $256.60   $256.60  
  Purchase #7 $249.64   11.638%   $278.6931   $278.69   $278.70   $278.70  
  7 purchase totals = $1,013.60       $1,110.6246   $1,110.62   $1,110.60   $1,110.60