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 $89.56   9.272%   $97.864   $97.86   $97.85   $97.90  
  Purchase #2 $221.47   3.259%   $228.6877   $228.69   $228.70   $228.70  
  Purchase #3 $65.56   6.537%   $69.8457   $69.85   $69.85   $69.80  
  Purchase #4 $247.45   3.663%   $256.5141   $256.51   $256.50   $256.50  
  Purchase #5 $56.29   13.569%   $63.928   $63.93   $63.95   $63.90  
  Purchase #6 $58.27   12.616%   $65.6213   $65.62   $65.60   $65.60  
  Purchase #7 $245.53   5.568%   $259.2011   $259.20   $259.20   $259.20  
  7 purchase totals = $984.13       $1,041.6619   $1,041.66   $1,041.65   $1,041.60