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 $32.68   12.782%   $36.8572   $36.86   $36.85   $36.90  
  Purchase #2 $140.74   10.629%   $155.6993   $155.70   $155.70   $155.70  
  Purchase #3 $17.31   3.704%   $17.9512   $17.95   $17.95   $18.00  
  Purchase #4 $207.45   6.791%   $221.5379   $221.54   $221.55   $221.50  
  Purchase #5 $68.59   3.275%   $70.8363   $70.84   $70.85   $70.80  
  Purchase #6 $192.50   7.640%   $207.207   $207.21   $207.20   $207.20  
  Purchase #7 $198.30   13.702%   $225.4711   $225.47   $225.45   $225.50  
  7 purchase totals = $857.57       $935.5600   $935.57   $935.55   $935.60