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 $241.72   8.822%   $263.0445   $263.04   $263.05   $263.00  
  Purchase #2 $49.73   11.252%   $55.3256   $55.33   $55.35   $55.30  
  Purchase #3 $80.30   11.421%   $89.4711   $89.47   $89.45   $89.50  
  Purchase #4 $165.62   9.412%   $181.2082   $181.21   $181.20   $181.20  
  Purchase #5 $242.63   10.499%   $268.1037   $268.10   $268.10   $268.10  
  Purchase #6 $72.31   9.628%   $79.272   $79.27   $79.25   $79.30  
  Purchase #7 $175.55   9.785%   $192.7276   $192.73   $192.75   $192.70  
  7 purchase totals = $1,027.86       $1,129.1527   $1,129.15   $1,129.15   $1,129.10