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 $119.32   13.418%   $135.3304   $135.33   $135.35   $135.30  
  Purchase #2 $141.40   9.833%   $155.3039   $155.30   $155.30   $155.30  
  Purchase #3 $124.44   9.791%   $136.6239   $136.62   $136.60   $136.60  
  Purchase #4 $248.85   13.112%   $281.4792   $281.48   $281.50   $281.50  
  Purchase #5 $145.59   11.715%   $162.6459   $162.65   $162.65   $162.60  
  Purchase #6 $125.50   12.120%   $140.7106   $140.71   $140.70   $140.70  
  Purchase #7 $53.77   6.531%   $57.2817   $57.28   $57.30   $57.30  
  7 purchase totals = $958.87       $1,069.3756   $1,069.37   $1,069.40   $1,069.30