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 $78.39   10.643%   $86.733   $86.73   $86.75   $86.70  
  Purchase #2 $74.76   12.848%   $84.3652   $84.37   $84.35   $84.40  
  Purchase #3 $43.39   10.815%   $48.0826   $48.08   $48.10   $48.10  
  Purchase #4 $50.93   6.173%   $54.0739   $54.07   $54.05   $54.10  
  Purchase #5 $243.92   12.731%   $274.9735   $274.97   $274.95   $275.00  
  Purchase #6 $72.53   11.813%   $81.098   $81.10   $81.10   $81.10  
  Purchase #7 $184.36   7.782%   $198.7069   $198.71   $198.70   $198.70  
  7 purchase totals = $748.28       $828.0331   $828.03   $828.00   $828.10