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 $91.83   11.213%   $102.1269   $102.13   $102.15   $102.10  
  Purchase #2 $232.44   9.435%   $254.3707   $254.37   $254.35   $254.40  
  Purchase #3 $230.69   12.408%   $259.314   $259.31   $259.30   $259.30  
  Purchase #4 $178.30   13.675%   $202.6825   $202.68   $202.70   $202.70  
  Purchase #5 $20.99   12.863%   $23.6899   $23.69   $23.70   $23.70  
  Purchase #6 $120.61   11.362%   $134.3137   $134.31   $134.30   $134.30  
  Purchase #7 $122.48   3.292%   $126.512   $126.51   $126.50   $126.50  
  7 purchase totals = $997.34       $1,103.0097   $1,103.00   $1,103.00   $1,103.00