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 $43.58   13.745%   $49.5701   $49.57   $49.55   $49.60  
  Purchase #2 $154.61   7.655%   $166.4454   $166.45   $166.45   $166.40  
  Purchase #3 $68.64   6.703%   $73.2409   $73.24   $73.25   $73.20  
  Purchase #4 $218.61   6.761%   $233.3902   $233.39   $233.40   $233.40  
  Purchase #5 $43.61   8.223%   $47.1961   $47.20   $47.20   $47.20  
  Purchase #6 $204.69   11.857%   $228.9601   $228.96   $228.95   $229.00  
  Purchase #7 $247.37   10.816%   $274.1255   $274.13   $274.15   $274.10  
  7 purchase totals = $981.11       $1,072.9283   $1,072.94   $1,072.95   $1,072.90