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 $240.48   10.803%   $266.4591   $266.46   $266.45   $266.50  
  Purchase #2 $188.44   6.826%   $201.3029   $201.30   $201.30   $201.30  
  Purchase #3 $159.35   6.717%   $170.0535   $170.05   $170.05   $170.10  
  Purchase #4 $111.33   4.863%   $116.744   $116.74   $116.75   $116.70  
  Purchase #5 $224.89   5.701%   $237.711   $237.71   $237.70   $237.70  
  Purchase #6 $189.94   10.592%   $210.0584   $210.06   $210.05   $210.10  
  Purchase #7 $123.32   4.318%   $128.645   $128.65   $128.65   $128.60  
  7 purchase totals = $1,237.75       $1,330.9739   $1,330.97   $1,330.95   $1,331.00