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 $97.71   13.551%   $110.9507   $110.95   $110.95   $111.00  
  Purchase #2 $54.73   3.804%   $56.8119   $56.81   $56.80   $56.80  
  Purchase #3 $153.80   8.848%   $167.4082   $167.41   $167.40   $167.40  
  Purchase #4 $18.88   3.738%   $19.5857   $19.59   $19.60   $19.60  
  Purchase #5 $235.55   7.834%   $254.003   $254.00   $254.00   $254.00  
  Purchase #6 $135.67   4.497%   $141.7711   $141.77   $141.75   $141.80  
  Purchase #7 $93.80   9.774%   $102.968   $102.97   $102.95   $103.00  
  7 purchase totals = $790.14       $853.4986   $853.50   $853.45   $853.60