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 $81.88   13.643%   $93.0509   $93.05   $93.05   $93.10  
  Purchase #2 $140.55   13.625%   $159.6999   $159.70   $159.70   $159.70  
  Purchase #3 $89.68   11.178%   $99.7044   $99.70   $99.70   $99.70  
  Purchase #4 $248.71   13.207%   $281.5571   $281.56   $281.55   $281.60  
  Purchase #5 $147.69   5.221%   $155.4009   $155.40   $155.40   $155.40  
  Purchase #6 $200.50   11.728%   $224.0146   $224.01   $224.00   $224.00  
  Purchase #7 $129.71   10.372%   $143.1635   $143.16   $143.15   $143.20  
  7 purchase totals = $1,038.72       $1,156.5913   $1,156.58   $1,156.55   $1,156.70