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 $150.46   9.861%   $165.2969   $165.30   $165.30   $165.30  
  Purchase #2 $158.94   8.597%   $172.6041   $172.60   $172.60   $172.60  
  Purchase #3 $244.75   3.653%   $253.6907   $253.69   $253.70   $253.70  
  Purchase #4 $187.39   8.534%   $203.3819   $203.38   $203.40   $203.40  
  Purchase #5 $183.51   10.417%   $202.6262   $202.63   $202.65   $202.60  
  Purchase #6 $227.37   3.816%   $236.0464   $236.05   $236.05   $236.00  
  Purchase #7 $20.51   8.435%   $22.24   $22.24   $22.25   $22.20  
  7 purchase totals = $1,172.93       $1,255.8862   $1,255.89   $1,255.95   $1,255.80