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 $143.27   7.506%   $154.0238   $154.02   $154.00   $154.00  
  Purchase #2 $95.58   7.472%   $102.7217   $102.72   $102.70   $102.70  
  Purchase #3 $23.70   12.624%   $26.6919   $26.69   $26.70   $26.70  
  Purchase #4 $195.32   5.258%   $205.5899   $205.59   $205.60   $205.60  
  Purchase #5 $61.40   12.346%   $68.9804   $68.98   $69.00   $69.00  
  Purchase #6 $249.57   12.812%   $281.5449   $281.54   $281.55   $281.50  
  Purchase #7 $22.51   5.160%   $23.6715   $23.67   $23.65   $23.70  
  7 purchase totals = $791.35       $863.2241   $863.21   $863.20   $863.20