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 $60.46   8.463%   $65.5767   $65.58   $65.60   $65.60  
  Purchase #2 $141.45   5.784%   $149.6315   $149.63   $149.65   $149.60  
  Purchase #3 $246.27   12.736%   $277.6349   $277.63   $277.65   $277.60  
  Purchase #4 $36.56   7.557%   $39.3228   $39.32   $39.30   $39.30  
  Purchase #5 $48.91   11.763%   $54.6633   $54.66   $54.65   $54.70  
  Purchase #6 $80.76   10.822%   $89.4998   $89.50   $89.50   $89.50  
  Purchase #7 $17.33   13.755%   $19.7137   $19.71   $19.70   $19.70  
  7 purchase totals = $631.74       $696.0427   $696.03   $696.05   $696.00