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 $49.31   9.471%   $53.9802   $53.98   $54.00   $54.00  
  Purchase #2 $226.66   9.832%   $248.9452   $248.95   $248.95   $248.90  
  Purchase #3 $169.26   13.185%   $191.5769   $191.58   $191.60   $191.60  
  Purchase #4 $42.52   8.387%   $46.0862   $46.09   $46.10   $46.10  
  Purchase #5 $100.57   7.338%   $107.9498   $107.95   $107.95   $107.90  
  Purchase #6 $227.48   8.694%   $247.2571   $247.26   $247.25   $247.30  
  Purchase #7 $211.70   11.186%   $235.3808   $235.38   $235.40   $235.40  
  7 purchase totals = $1,027.50       $1,131.1762   $1,131.19   $1,131.25   $1,131.20