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 $68.46   8.493%   $74.2743   $74.27   $74.25   $74.30  
  Purchase #2 $219.27   7.379%   $235.4499   $235.45   $235.45   $235.40  
  Purchase #3 $107.48   13.435%   $121.9199   $121.92   $121.90   $121.90  
  Purchase #4 $129.34   6.120%   $137.2556   $137.26   $137.25   $137.30  
  Purchase #5 $132.82   13.142%   $150.2752   $150.28   $150.30   $150.30  
  Purchase #6 $129.79   12.773%   $146.3681   $146.37   $146.35   $146.40  
  Purchase #7 $169.75   9.594%   $186.0358   $186.04   $186.05   $186.00  
  7 purchase totals = $956.91       $1,051.5788   $1,051.59   $1,051.55   $1,051.60