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 $152.76   7.204%   $163.7648   $163.76   $163.75   $163.80  
  Purchase #2 $172.38   11.802%   $192.7243   $192.72   $192.70   $192.70  
  Purchase #3 $83.75   4.768%   $87.7432   $87.74   $87.75   $87.70  
  Purchase #4 $193.79   9.176%   $211.5722   $211.57   $211.55   $211.60  
  Purchase #5 $69.89   12.340%   $78.5144   $78.51   $78.50   $78.50  
  Purchase #6 $27.62   13.354%   $31.3084   $31.31   $31.30   $31.30  
  Purchase #7 $237.44   7.869%   $256.1242   $256.12   $256.10   $256.10  
  7 purchase totals = $937.63       $1,021.7515   $1,021.73   $1,021.65   $1,021.70