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 $56.43   8.180%   $61.046   $61.05   $61.05   $61.00  
  Purchase #2 $183.44   12.310%   $206.0215   $206.02   $206.00   $206.00  
  Purchase #3 $183.76   6.413%   $195.5445   $195.54   $195.55   $195.50  
  Purchase #4 $58.83   10.778%   $65.1707   $65.17   $65.15   $65.20  
  Purchase #5 $36.95   7.218%   $39.6171   $39.62   $39.60   $39.60  
  Purchase #6 $174.36   8.434%   $189.0655   $189.07   $189.05   $189.10  
  Purchase #7 $220.58   13.257%   $249.8223   $249.82   $249.80   $249.80  
  7 purchase totals = $914.35       $1,006.2876   $1,006.29   $1,006.20   $1,006.20