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 $185.87   8.709%   $202.0574   $202.06   $202.05   $202.10  
  Purchase #2 $5.91   12.191%   $6.6305   $6.63   $6.65   $6.60  
  Purchase #3 $150.77   11.622%   $168.2925   $168.29   $168.30   $168.30  
  Purchase #4 $55.51   5.219%   $58.4071   $58.41   $58.40   $58.40  
  Purchase #5 $213.60   9.676%   $234.2679   $234.27   $234.25   $234.30  
  Purchase #6 $48.36   8.732%   $52.5828   $52.58   $52.60   $52.60  
  Purchase #7 $54.57   13.302%   $61.8289   $61.83   $61.85   $61.80  
  7 purchase totals = $714.59       $784.0671   $784.07   $784.10   $784.10