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 $232.27   4.859%   $243.556   $243.56   $243.55   $243.60  
  Purchase #2 $34.86   6.482%   $37.1196   $37.12   $37.10   $37.10  
  Purchase #3 $59.71   7.827%   $64.3835   $64.38   $64.40   $64.40  
  Purchase #4 $68.67   9.641%   $75.2905   $75.29   $75.30   $75.30  
  Purchase #5 $175.45   5.214%   $184.598   $184.60   $184.60   $184.60  
  Purchase #6 $79.75   5.308%   $83.9831   $83.98   $84.00   $84.00  
  Purchase #7 $192.32   5.274%   $202.463   $202.46   $202.45   $202.50  
  7 purchase totals = $843.03       $891.3937   $891.39   $891.40   $891.50