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 $46.72   13.434%   $52.9964   $53.00   $53.00   $53.00  
  Purchase #2 $193.95   11.124%   $215.525   $215.53   $215.55   $215.50  
  Purchase #3 $126.96   3.159%   $130.9707   $130.97   $130.95   $131.00  
  Purchase #4 $179.79   12.285%   $201.8772   $201.88   $201.90   $201.90  
  Purchase #5 $52.45   9.362%   $57.3604   $57.36   $57.35   $57.40  
  Purchase #6 $84.80   12.759%   $95.6196   $95.62   $95.60   $95.60  
  Purchase #7 $84.25   7.511%   $90.578   $90.58   $90.60   $90.60  
  7 purchase totals = $768.92       $844.9273   $844.94   $844.95   $845.00