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 $58.54   5.842%   $61.9599   $61.96   $61.95   $62.00  
  Purchase #2 $211.52   11.501%   $235.8469   $235.85   $235.85   $235.80  
  Purchase #3 $8.51   9.235%   $9.2959   $9.30   $9.30   $9.30  
  Purchase #4 $203.38   10.387%   $224.5051   $224.51   $224.50   $224.50  
  Purchase #5 $83.25   5.120%   $87.5124   $87.51   $87.50   $87.50  
  Purchase #6 $125.53   9.705%   $137.7127   $137.71   $137.70   $137.70  
  Purchase #7 $233.50   3.753%   $242.2633   $242.26   $242.25   $242.30  
  7 purchase totals = $924.23       $999.0962   $999.10   $999.05   $999.10