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 $120.80   11.132%   $134.2475   $134.25   $134.25   $134.20  
  Purchase #2 $128.96   12.648%   $145.2709   $145.27   $145.25   $145.30  
  Purchase #3 $205.91   8.103%   $222.5949   $222.59   $222.60   $222.60  
  Purchase #4 $24.66   5.627%   $26.0476   $26.05   $26.05   $26.00  
  Purchase #5 $75.76   8.752%   $82.3905   $82.39   $82.40   $82.40  
  Purchase #6 $232.94   8.225%   $252.0993   $252.10   $252.10   $252.10  
  Purchase #7 $135.42   12.350%   $152.1444   $152.14   $152.15   $152.10  
  7 purchase totals = $924.45       $1,014.7951   $1,014.79   $1,014.80   $1,014.70