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 $82.54   5.787%   $87.3166   $87.32   $87.30   $87.30  
  Purchase #2 $200.57   5.592%   $211.7859   $211.79   $211.80   $211.80  
  Purchase #3 $23.44   6.634%   $24.995   $25.00   $25.00   $25.00  
  Purchase #4 $181.26   10.607%   $200.4862   $200.49   $200.50   $200.50  
  Purchase #5 $238.27   12.349%   $267.694   $267.69   $267.70   $267.70  
  Purchase #6 $188.36   5.336%   $198.4109   $198.41   $198.40   $198.40  
  Purchase #7 $248.48   12.587%   $279.7562   $279.76   $279.75   $279.80  
  7 purchase totals = $1,162.92       $1,270.4448   $1,270.46   $1,270.45   $1,270.50