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 $43.27   10.242%   $47.7017   $47.70   $47.70   $47.70  
  Purchase #2 $148.80   13.158%   $168.3791   $168.38   $168.40   $168.40  
  Purchase #3 $58.29   7.796%   $62.8343   $62.83   $62.85   $62.80  
  Purchase #4 $125.27   8.396%   $135.7877   $135.79   $135.80   $135.80  
  Purchase #5 $76.72   12.160%   $86.0492   $86.05   $86.05   $86.00  
  Purchase #6 $232.53   12.127%   $260.7289   $260.73   $260.75   $260.70  
  Purchase #7 $229.69   12.142%   $257.579   $257.58   $257.60   $257.60  
  7 purchase totals = $914.57       $1,019.0599   $1,019.06   $1,019.15   $1,019.00