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 $187.49   10.771%   $207.6845   $207.68   $207.70   $207.70  
  Purchase #2 $26.25   4.562%   $27.4475   $27.45   $27.45   $27.40  
  Purchase #3 $106.57   12.435%   $119.822   $119.82   $119.80   $119.80  
  Purchase #4 $228.78   5.674%   $241.761   $241.76   $241.75   $241.80  
  Purchase #5 $107.88   10.334%   $119.0283   $119.03   $119.05   $119.00  
  Purchase #6 $236.81   11.846%   $264.8625   $264.86   $264.85   $264.90  
  Purchase #7 $68.49   7.438%   $73.5843   $73.58   $73.60   $73.60  
  7 purchase totals = $962.27       $1,054.1901   $1,054.18   $1,054.20   $1,054.20