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 $210.55   11.565%   $234.9001   $234.90   $234.90   $234.90  
  Purchase #2 $194.53   4.592%   $203.4628   $203.46   $203.45   $203.50  
  Purchase #3 $74.41   7.226%   $79.7869   $79.79   $79.80   $79.80  
  Purchase #4 $152.91   5.135%   $160.7619   $160.76   $160.75   $160.80  
  Purchase #5 $205.58   13.357%   $233.0393   $233.04   $233.05   $233.00  
  Purchase #6 $44.95   10.256%   $49.5601   $49.56   $49.55   $49.60  
  Purchase #7 $179.70   3.843%   $186.6059   $186.61   $186.60   $186.60  
  7 purchase totals = $1,062.63       $1,148.1170   $1,148.12   $1,148.10   $1,148.20