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 $30.58   9.797%   $33.5759   $33.58   $33.60   $33.60  
  Purchase #2 $79.59   12.528%   $89.561   $89.56   $89.55   $89.60  
  Purchase #3 $122.51   3.469%   $126.7599   $126.76   $126.75   $126.80  
  Purchase #4 $62.64   5.232%   $65.9173   $65.92   $65.90   $65.90  
  Purchase #5 $118.72   6.372%   $126.2848   $126.28   $126.30   $126.30  
  Purchase #6 $208.73   13.785%   $237.5034   $237.50   $237.50   $237.50  
  Purchase #7 $82.97   5.730%   $87.7242   $87.72   $87.70   $87.70  
  7 purchase totals = $705.74       $767.3265   $767.32   $767.30   $767.40