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 $181.95   10.703%   $201.4241   $201.42   $201.40   $201.40  
  Purchase #2 $174.31   5.214%   $183.3985   $183.40   $183.40   $183.40  
  Purchase #3 $156.26   11.528%   $174.2737   $174.27   $174.25   $174.30  
  Purchase #4 $31.82   5.247%   $33.4896   $33.49   $33.50   $33.50  
  Purchase #5 $96.80   5.251%   $101.883   $101.88   $101.90   $101.90  
  Purchase #6 $160.42   7.384%   $172.2654   $172.27   $172.25   $172.30  
  Purchase #7 $47.39   5.192%   $49.8505   $49.85   $49.85   $49.90  
  7 purchase totals = $848.95       $916.5848   $916.58   $916.55   $916.70