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 $182.80   11.461%   $203.7507   $203.75   $203.75   $203.80  
  Purchase #2 $38.78   9.714%   $42.5471   $42.55   $42.55   $42.50  
  Purchase #3 $75.89   9.363%   $82.9956   $83.00   $83.00   $83.00  
  Purchase #4 $53.59   6.863%   $57.2679   $57.27   $57.25   $57.30  
  Purchase #5 $194.99   11.585%   $217.5796   $217.58   $217.60   $217.60  
  Purchase #6 $230.80   4.226%   $240.5536   $240.55   $240.55   $240.60  
  Purchase #7 $219.57   5.689%   $232.0613   $232.06   $232.05   $232.10  
  7 purchase totals = $996.42       $1,076.7558   $1,076.76   $1,076.75   $1,076.90