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 $197.99   5.239%   $208.3627   $208.36   $208.35   $208.40  
  Purchase #2 $150.82   11.303%   $167.8672   $167.87   $167.85   $167.90  
  Purchase #3 $83.45   13.469%   $94.6899   $94.69   $94.70   $94.70  
  Purchase #4 $22.41   13.375%   $25.4073   $25.41   $25.40   $25.40  
  Purchase #5 $200.69   12.661%   $226.0994   $226.10   $226.10   $226.10  
  Purchase #6 $197.68   11.835%   $221.0754   $221.08   $221.10   $221.10  
  Purchase #7 $29.66   9.850%   $32.5815   $32.58   $32.60   $32.60  
  7 purchase totals = $882.70       $976.0834   $976.09   $976.10   $976.20