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 $151.33   6.816%   $161.6447   $161.64   $161.65   $161.60  
  Purchase #2 $68.32   13.596%   $77.6088   $77.61   $77.60   $77.60  
  Purchase #3 $24.98   6.835%   $26.6874   $26.69   $26.70   $26.70  
  Purchase #4 $109.81   8.145%   $118.754   $118.75   $118.75   $118.80  
  Purchase #5 $166.66   9.145%   $181.9011   $181.90   $181.90   $181.90  
  Purchase #6 $183.57   11.406%   $204.508   $204.51   $204.50   $204.50  
  Purchase #7 $123.56   13.253%   $139.9354   $139.94   $139.95   $139.90  
  7 purchase totals = $828.23       $911.0394   $911.04   $911.05   $911.00