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 $137.97   4.668%   $144.4104   $144.41   $144.40   $144.40  
  Purchase #2 $116.74   13.453%   $132.445   $132.45   $132.45   $132.40  
  Purchase #3 $181.25   9.372%   $198.2368   $198.24   $198.25   $198.20  
  Purchase #4 $202.86   7.428%   $217.9284   $217.93   $217.95   $217.90  
  Purchase #5 $84.58   6.285%   $89.8959   $89.90   $89.90   $89.90  
  Purchase #6 $246.49   5.377%   $259.7438   $259.74   $259.75   $259.70  
  Purchase #7 $49.88   10.510%   $55.1224   $55.12   $55.10   $55.10  
  7 purchase totals = $1,019.77       $1,097.7827   $1,097.79   $1,097.80   $1,097.60