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 $148.30   12.592%   $166.9739   $166.97   $166.95   $167.00  
  Purchase #2 $224.57   5.290%   $236.4498   $236.45   $236.45   $236.40  
  Purchase #3 $201.93   5.627%   $213.2926   $213.29   $213.30   $213.30  
  Purchase #4 $217.39   8.196%   $235.2073   $235.21   $235.20   $235.20  
  Purchase #5 $135.72   12.448%   $152.6144   $152.61   $152.60   $152.60  
  Purchase #6 $239.25   11.422%   $266.5771   $266.58   $266.60   $266.60  
  Purchase #7 $87.96   5.206%   $92.5392   $92.54   $92.55   $92.50  
  7 purchase totals = $1,255.12       $1,363.6543   $1,363.65   $1,363.65   $1,363.60