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 $189.92   11.189%   $211.1701   $211.17   $211.15   $211.20  
  Purchase #2 $205.57   9.399%   $224.8915   $224.89   $224.90   $224.90  
  Purchase #3 $100.92   9.679%   $110.688   $110.69   $110.70   $110.70  
  Purchase #4 $53.25   13.781%   $60.5884   $60.59   $60.60   $60.60  
  Purchase #5 $164.48   12.751%   $185.4528   $185.45   $185.45   $185.50  
  Purchase #6 $190.91   6.538%   $203.3917   $203.39   $203.40   $203.40  
  Purchase #7 $53.35   5.625%   $56.3509   $56.35   $56.35   $56.40  
  7 purchase totals = $958.40       $1,052.5334   $1,052.53   $1,052.55   $1,052.70