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 $91.51   5.436%   $96.4845   $96.48   $96.50   $96.50  
  Purchase #2 $103.39   7.271%   $110.9075   $110.91   $110.90   $110.90  
  Purchase #3 $200.27   3.468%   $207.2154   $207.22   $207.20   $207.20  
  Purchase #4 $77.49   10.738%   $85.8109   $85.81   $85.80   $85.80  
  Purchase #5 $189.82   6.558%   $202.2684   $202.27   $202.25   $202.30  
  Purchase #6 $175.50   5.576%   $185.2859   $185.29   $185.30   $185.30  
  Purchase #7 $173.76   4.117%   $180.9137   $180.91   $180.90   $180.90  
  7 purchase totals = $1,011.74       $1,068.8863   $1,068.89   $1,068.85   $1,068.90