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 $207.57   8.613%   $225.448   $225.45   $225.45   $225.40  
  Purchase #2 $107.35   10.500%   $118.6218   $118.62   $118.60   $118.60  
  Purchase #3 $208.38   12.314%   $234.0399   $234.04   $234.05   $234.00  
  Purchase #4 $223.57   3.148%   $230.608   $230.61   $230.60   $230.60  
  Purchase #5 $190.96   8.777%   $207.7206   $207.72   $207.70   $207.70  
  Purchase #6 $62.46   9.727%   $68.5355   $68.54   $68.55   $68.50  
  Purchase #7 $145.87   13.386%   $165.3962   $165.40   $165.40   $165.40  
  7 purchase totals = $1,146.16       $1,250.3700   $1,250.38   $1,250.35   $1,250.20