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 $56.26   9.380%   $61.5372   $61.54   $61.55   $61.50  
  Purchase #2 $209.91   11.259%   $233.5438   $233.54   $233.55   $233.50  
  Purchase #3 $203.87   6.587%   $217.2989   $217.30   $217.30   $217.30  
  Purchase #4 $207.50   6.435%   $220.8526   $220.85   $220.85   $220.90  
  Purchase #5 $78.43   11.270%   $87.2691   $87.27   $87.25   $87.30  
  Purchase #6 $132.49   9.766%   $145.429   $145.43   $145.45   $145.40  
  Purchase #7 $56.39   9.575%   $61.7893   $61.79   $61.80   $61.80  
  7 purchase totals = $944.85       $1,027.7199   $1,027.72   $1,027.75   $1,027.70