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 $157.41   11.357%   $175.2871   $175.29   $175.30   $175.30  
  Purchase #2 $28.37   9.466%   $31.0555   $31.06   $31.05   $31.10  
  Purchase #3 $213.28   12.519%   $239.9805   $239.98   $240.00   $240.00  
  Purchase #4 $244.50   5.534%   $258.0306   $258.03   $258.05   $258.00  
  Purchase #5 $50.35   5.430%   $53.084   $53.08   $53.10   $53.10  
  Purchase #6 $41.34   3.182%   $42.6554   $42.66   $42.65   $42.70  
  Purchase #7 $221.58   5.469%   $233.6982   $233.70   $233.70   $233.70  
  7 purchase totals = $956.83       $1,033.7913   $1,033.80   $1,033.85   $1,033.90