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 $144.87   5.799%   $153.271   $153.27   $153.25   $153.30  
  Purchase #2 $198.47   13.211%   $224.6899   $224.69   $224.70   $224.70  
  Purchase #3 $181.86   8.614%   $197.5254   $197.53   $197.55   $197.50  
  Purchase #4 $119.91   12.824%   $135.2873   $135.29   $135.30   $135.30  
  Purchase #5 $8.45   6.577%   $9.0058   $9.01   $9.00   $9.00  
  Purchase #6 $59.65   8.498%   $64.7191   $64.72   $64.70   $64.70  
  Purchase #7 $59.71   12.574%   $67.2179   $67.22   $67.20   $67.20  
  7 purchase totals = $772.92       $851.7164   $851.73   $851.70   $851.70