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 $202.64   6.611%   $216.0365   $216.04   $216.05   $216.00  
  Purchase #2 $151.96   3.367%   $157.0765   $157.08   $157.10   $157.10  
  Purchase #3 $111.88   10.363%   $123.4741   $123.47   $123.45   $123.50  
  Purchase #4 $41.77   13.803%   $47.5355   $47.54   $47.55   $47.50  
  Purchase #5 $238.94   7.264%   $256.2966   $256.30   $256.30   $256.30  
  Purchase #6 $235.28   13.861%   $267.8922   $267.89   $267.90   $267.90  
  Purchase #7 $228.42   6.176%   $242.5272   $242.53   $242.55   $242.50  
  7 purchase totals = $1,210.89       $1,310.8386   $1,310.85   $1,310.90   $1,310.80