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 $84.90   11.220%   $94.4258   $94.43   $94.45   $94.40  
  Purchase #2 $231.51   6.585%   $246.7549   $246.75   $246.75   $246.80  
  Purchase #3 $129.69   5.564%   $136.906   $136.91   $136.90   $136.90  
  Purchase #4 $151.99   10.384%   $167.7726   $167.77   $167.75   $167.80  
  Purchase #5 $26.49   11.639%   $29.5732   $29.57   $29.55   $29.60  
  Purchase #6 $149.65   3.476%   $154.8518   $154.85   $154.85   $154.90  
  Purchase #7 $190.70   12.565%   $214.6615   $214.66   $214.65   $214.70  
  7 purchase totals = $964.93       $1,044.9458   $1,044.94   $1,044.90   $1,045.10