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 $209.98   10.457%   $231.9376   $231.94   $231.95   $231.90  
  Purchase #2 $69.69   11.643%   $77.804   $77.80   $77.80   $77.80  
  Purchase #3 $169.71   5.803%   $179.5583   $179.56   $179.55   $179.60  
  Purchase #4 $103.79   10.155%   $114.3299   $114.33   $114.35   $114.30  
  Purchase #5 $26.86   10.464%   $29.6706   $29.67   $29.65   $29.70  
  Purchase #6 $248.57   11.145%   $276.2731   $276.27   $276.25   $276.30  
  Purchase #7 $46.39   9.368%   $50.7358   $50.74   $50.75   $50.70  
  7 purchase totals = $874.99       $960.3093   $960.31   $960.30   $960.30