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 $185.65   12.569%   $208.9843   $208.98   $209.00   $209.00  
  Purchase #2 $58.69   5.448%   $61.8874   $61.89   $61.90   $61.90  
  Purchase #3 $225.42   9.465%   $246.756   $246.76   $246.75   $246.80  
  Purchase #4 $184.51   11.124%   $205.0349   $205.03   $205.05   $205.00  
  Purchase #5 $144.90   7.116%   $155.2111   $155.21   $155.20   $155.20  
  Purchase #6 $121.77   5.641%   $128.639   $128.64   $128.65   $128.60  
  Purchase #7 $104.89   11.530%   $116.9838   $116.98   $117.00   $117.00  
  7 purchase totals = $1,025.83       $1,123.4965   $1,123.49   $1,123.55   $1,123.50