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 $228.38   12.764%   $257.5304   $257.53   $257.55   $257.50  
  Purchase #2 $43.44   12.118%   $48.7041   $48.70   $48.70   $48.70  
  Purchase #3 $27.62   7.272%   $29.6285   $29.63   $29.65   $29.60  
  Purchase #4 $205.96   10.595%   $227.7815   $227.78   $227.80   $227.80  
  Purchase #5 $168.41   12.699%   $189.7964   $189.80   $189.80   $189.80  
  Purchase #6 $199.66   13.678%   $226.9695   $226.97   $226.95   $227.00  
  Purchase #7 $80.85   8.257%   $87.5258   $87.53   $87.55   $87.50  
  7 purchase totals = $954.32       $1,067.9362   $1,067.94   $1,068.00   $1,067.90