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 $197.77   13.236%   $223.9468   $223.95   $223.95   $223.90  
  Purchase #2 $24.52   7.836%   $26.4414   $26.44   $26.45   $26.40  
  Purchase #3 $234.92   13.319%   $266.209   $266.21   $266.20   $266.20  
  Purchase #4 $79.94   9.112%   $87.2241   $87.22   $87.20   $87.20  
  Purchase #5 $248.94   5.624%   $262.9404   $262.94   $262.95   $262.90  
  Purchase #6 $107.45   8.334%   $116.4049   $116.40   $116.40   $116.40  
  Purchase #7 $191.42   5.222%   $201.416   $201.42   $201.40   $201.40  
  7 purchase totals = $1,084.96       $1,184.5826   $1,184.58   $1,184.55   $1,184.40