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 $88.88   4.118%   $92.5401   $92.54   $92.55   $92.50  
  Purchase #2 $171.86   5.337%   $181.0322   $181.03   $181.05   $181.00  
  Purchase #3 $242.49   5.481%   $255.7809   $255.78   $255.80   $255.80  
  Purchase #4 $134.53   10.585%   $148.77   $148.77   $148.75   $148.80  
  Purchase #5 $41.92   13.569%   $47.6081   $47.61   $47.60   $47.60  
  Purchase #6 $152.49   5.307%   $160.5826   $160.58   $160.60   $160.60  
  Purchase #7 $119.93   7.286%   $128.6681   $128.67   $128.65   $128.70  
  7 purchase totals = $952.10       $1,014.9820   $1,014.98   $1,015.00   $1,015.00