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 $54.31   13.822%   $61.8167   $61.82   $61.80   $61.80  
  Purchase #2 $209.45   12.801%   $236.2617   $236.26   $236.25   $236.30  
  Purchase #3 $174.28   13.506%   $197.8183   $197.82   $197.80   $197.80  
  Purchase #4 $25.58   8.811%   $27.8339   $27.83   $27.85   $27.80  
  Purchase #5 $226.96   9.386%   $248.2625   $248.26   $248.25   $248.30  
  Purchase #6 $244.40   11.679%   $272.9435   $272.94   $272.95   $272.90  
  Purchase #7 $207.97   11.377%   $231.6307   $231.63   $231.65   $231.60  
  7 purchase totals = $1,142.95       $1,276.5673   $1,276.56   $1,276.55   $1,276.50