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 $58.54   4.750%   $61.3207   $61.32   $61.30   $61.30  
  Purchase #2 $184.96   13.246%   $209.4598   $209.46   $209.45   $209.50  
  Purchase #3 $8.65   5.780%   $9.15   $9.15   $9.15   $9.20  
  Purchase #4 $97.48   10.107%   $107.3323   $107.33   $107.35   $107.30  
  Purchase #5 $239.70   4.553%   $250.6135   $250.61   $250.60   $250.60  
  Purchase #6 $187.70   5.112%   $197.2952   $197.30   $197.30   $197.30  
  Purchase #7 $128.42   11.158%   $142.7491   $142.75   $142.75   $142.70  
  7 purchase totals = $905.45       $977.9206   $977.92   $977.90   $977.90