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 $65.37   4.812%   $68.5156   $68.52   $68.50   $68.50  
  Purchase #2 $207.36   9.166%   $226.3666   $226.37   $226.35   $226.40  
  Purchase #3 $190.44   9.121%   $207.81   $207.81   $207.80   $207.80  
  Purchase #4 $162.91   11.710%   $181.9868   $181.99   $182.00   $182.00  
  Purchase #5 $147.31   11.810%   $164.7073   $164.71   $164.70   $164.70  
  Purchase #6 $181.80   7.443%   $195.3314   $195.33   $195.35   $195.30  
  Purchase #7 $205.94   3.778%   $213.7204   $213.72   $213.70   $213.70  
  7 purchase totals = $1,161.13       $1,258.4381   $1,258.45   $1,258.40   $1,258.40