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 $49.49   13.210%   $56.0276   $56.03   $56.05   $56.00  
  Purchase #2 $193.59   4.726%   $202.7391   $202.74   $202.75   $202.70  
  Purchase #3 $216.89   8.600%   $235.5425   $235.54   $235.55   $235.50  
  Purchase #4 $208.60   13.230%   $236.1978   $236.20   $236.20   $236.20  
  Purchase #5 $171.55   6.372%   $182.4812   $182.48   $182.50   $182.50  
  Purchase #6 $24.39   6.568%   $25.9919   $25.99   $26.00   $26.00  
  Purchase #7 $166.48   3.807%   $172.8179   $172.82   $172.80   $172.80  
  7 purchase totals = $1,030.99       $1,111.7980   $1,111.80   $1,111.85   $1,111.70