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 $63.62   11.457%   $70.9089   $70.91   $70.90   $70.90  
  Purchase #2 $229.55   3.356%   $237.2537   $237.25   $237.25   $237.30  
  Purchase #3 $128.35   12.577%   $144.4926   $144.49   $144.50   $144.50  
  Purchase #4 $236.87   9.449%   $259.2518   $259.25   $259.25   $259.30  
  Purchase #5 $214.67   6.540%   $228.7094   $228.71   $228.70   $228.70  
  Purchase #6 $211.37   5.216%   $222.3951   $222.40   $222.40   $222.40  
  Purchase #7 $138.74   4.511%   $144.9986   $145.00   $145.00   $145.00  
  7 purchase totals = $1,223.17       $1,308.0101   $1,308.01   $1,308.00   $1,308.10