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 $87.94   8.381%   $95.3103   $95.31   $95.30   $95.30  
  Purchase #2 $238.78   12.775%   $269.2841   $269.28   $269.30   $269.30  
  Purchase #3 $98.28   13.768%   $111.8112   $111.81   $111.80   $111.80  
  Purchase #4 $104.32   8.103%   $112.773   $112.77   $112.75   $112.80  
  Purchase #5 $227.29   3.530%   $235.3133   $235.31   $235.30   $235.30  
  Purchase #6 $241.96   9.753%   $265.5584   $265.56   $265.55   $265.60  
  Purchase #7 $121.77   7.180%   $130.5131   $130.51   $130.50   $130.50  
  7 purchase totals = $1,120.34       $1,220.5634   $1,220.55   $1,220.50   $1,220.60