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 $169.53   13.621%   $192.6217   $192.62   $192.60   $192.60  
  Purchase #2 $131.79   3.839%   $136.8494   $136.85   $136.85   $136.80  
  Purchase #3 $181.59   6.368%   $193.1537   $193.15   $193.15   $193.20  
  Purchase #4 $221.34   11.870%   $247.6131   $247.61   $247.60   $247.60  
  Purchase #5 $223.39   4.743%   $233.9854   $233.99   $234.00   $234.00  
  Purchase #6 $52.80   12.812%   $59.5647   $59.56   $59.55   $59.60  
  Purchase #7 $40.87   13.518%   $46.3948   $46.39   $46.40   $46.40  
  7 purchase totals = $1,021.31       $1,110.1828   $1,110.17   $1,110.15   $1,110.20