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 $236.58   13.209%   $267.8299   $267.83   $267.85   $267.80  
  Purchase #2 $182.59   11.294%   $203.2117   $203.21   $203.20   $203.20  
  Purchase #3 $61.27   10.648%   $67.794   $67.79   $67.80   $67.80  
  Purchase #4 $243.97   11.687%   $272.4828   $272.48   $272.50   $272.50  
  Purchase #5 $208.92   11.755%   $233.4785   $233.48   $233.50   $233.50  
  Purchase #6 $54.65   10.147%   $60.1953   $60.20   $60.20   $60.20  
  Purchase #7 $241.34   12.706%   $272.0047   $272.00   $272.00   $272.00  
  7 purchase totals = $1,229.32       $1,376.9969   $1,376.99   $1,377.05   $1,377.00