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 $56.31   9.324%   $61.5603   $61.56   $61.55   $61.60  
  Purchase #2 $226.79   11.285%   $252.3833   $252.38   $252.40   $252.40  
  Purchase #3 $147.75   9.216%   $161.3666   $161.37   $161.35   $161.40  
  Purchase #4 $194.96   12.402%   $219.1389   $219.14   $219.15   $219.10  
  Purchase #5 $248.85   8.329%   $269.5767   $269.58   $269.60   $269.60  
  Purchase #6 $129.67   13.229%   $146.824   $146.82   $146.80   $146.80  
  Purchase #7 $63.97   8.868%   $69.6429   $69.64   $69.65   $69.60  
  7 purchase totals = $1,068.30       $1,180.4927   $1,180.49   $1,180.50   $1,180.50