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 $190.92   6.343%   $203.0301   $203.03   $203.05   $203.00  
  Purchase #2 $177.57   8.179%   $192.0935   $192.09   $192.10   $192.10  
  Purchase #3 $59.38   11.592%   $66.2633   $66.26   $66.25   $66.30  
  Purchase #4 $95.87   7.383%   $102.9481   $102.95   $102.95   $102.90  
  Purchase #5 $186.37   13.140%   $210.859   $210.86   $210.85   $210.90  
  Purchase #6 $168.61   7.581%   $181.3923   $181.39   $181.40   $181.40  
  Purchase #7 $44.39   11.678%   $49.5739   $49.57   $49.55   $49.60  
  7 purchase totals = $923.11       $1,006.1602   $1,006.15   $1,006.15   $1,006.20