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 $94.53   10.730%   $104.6731   $104.67   $104.65   $104.70  
  Purchase #2 $207.73   10.736%   $230.0319   $230.03   $230.05   $230.00  
  Purchase #3 $10.75   12.459%   $12.0893   $12.09   $12.10   $12.10  
  Purchase #4 $174.39   5.724%   $184.3721   $184.37   $184.35   $184.40  
  Purchase #5 $144.88   12.529%   $163.032   $163.03   $163.05   $163.00  
  Purchase #6 $193.99   12.853%   $218.9235   $218.92   $218.90   $218.90  
  Purchase #7 $138.85   6.143%   $147.3796   $147.38   $147.40   $147.40  
  7 purchase totals = $965.12       $1,060.5015   $1,060.49   $1,060.50   $1,060.50