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 $45.93   12.265%   $51.5633   $51.56   $51.55   $51.60  
  Purchase #2 $248.30   9.143%   $271.0021   $271.00   $271.00   $271.00  
  Purchase #3 $42.56   9.525%   $46.6138   $46.61   $46.60   $46.60  
  Purchase #4 $106.87   8.154%   $115.5842   $115.58   $115.60   $115.60  
  Purchase #5 $235.26   5.478%   $248.1475   $248.15   $248.15   $248.10  
  Purchase #6 $31.76   6.142%   $33.7107   $33.71   $33.70   $33.70  
  Purchase #7 $117.44   9.815%   $128.9667   $128.97   $128.95   $129.00  
  7 purchase totals = $828.12       $895.5883   $895.58   $895.55   $895.60