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 $176.65   11.358%   $196.7139   $196.71   $196.70   $196.70  
  Purchase #2 $88.78   10.612%   $98.2013   $98.20   $98.20   $98.20  
  Purchase #3 $85.98   6.848%   $91.8679   $91.87   $91.85   $91.90  
  Purchase #4 $179.46   5.695%   $189.6802   $189.68   $189.70   $189.70  
  Purchase #5 $97.26   11.196%   $108.1492   $108.15   $108.15   $108.10  
  Purchase #6 $191.84   12.811%   $216.4166   $216.42   $216.40   $216.40  
  Purchase #7 $101.50   3.693%   $105.2484   $105.25   $105.25   $105.20  
  7 purchase totals = $921.47       $1,006.2775   $1,006.28   $1,006.25   $1,006.20