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 $43.25   13.802%   $49.2194   $49.22   $49.20   $49.20  
  Purchase #2 $97.58   7.425%   $104.8253   $104.83   $104.85   $104.80  
  Purchase #3 $79.88   12.302%   $89.7068   $89.71   $89.70   $89.70  
  Purchase #4 $211.83   7.645%   $228.0244   $228.02   $228.00   $228.00  
  Purchase #5 $175.48   12.583%   $197.5606   $197.56   $197.55   $197.60  
  Purchase #6 $176.70   3.846%   $183.4959   $183.50   $183.50   $183.50  
  Purchase #7 $189.73   6.302%   $201.6868   $201.69   $201.70   $201.70  
  7 purchase totals = $974.45       $1,054.5192   $1,054.53   $1,054.50   $1,054.50