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 $221.51   13.747%   $251.961   $251.96   $251.95   $252.00  
  Purchase #2 $45.39   11.430%   $50.5781   $50.58   $50.60   $50.60  
  Purchase #3 $180.49   7.627%   $194.256   $194.26   $194.25   $194.30  
  Purchase #4 $156.28   11.581%   $174.3788   $174.38   $174.40   $174.40  
  Purchase #5 $150.54   9.274%   $164.5011   $164.50   $164.50   $164.50  
  Purchase #6 $166.77   9.564%   $182.7199   $182.72   $182.70   $182.70  
  Purchase #7 $54.82   7.492%   $58.9271   $58.93   $58.95   $58.90  
  7 purchase totals = $975.80       $1,077.3220   $1,077.33   $1,077.35   $1,077.40