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 $87.84   11.517%   $97.9565   $97.96   $97.95   $98.00  
  Purchase #2 $196.62   3.464%   $203.4309   $203.43   $203.45   $203.40  
  Purchase #3 $86.92   13.724%   $98.8489   $98.85   $98.85   $98.80  
  Purchase #4 $246.91   4.199%   $257.2778   $257.28   $257.30   $257.30  
  Purchase #5 $166.87   4.113%   $173.7334   $173.73   $173.75   $173.70  
  Purchase #6 $218.60   12.518%   $245.9643   $245.96   $245.95   $246.00  
  Purchase #7 $90.49   8.287%   $97.9889   $97.99   $98.00   $98.00  
  7 purchase totals = $1,094.25       $1,175.2007   $1,175.20   $1,175.25   $1,175.20