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 $56.40   4.668%   $59.0328   $59.03   $59.05   $59.00  
  Purchase #2 $159.93   11.786%   $178.7793   $178.78   $178.80   $178.80  
  Purchase #3 $245.86   12.860%   $277.4776   $277.48   $277.50   $277.50  
  Purchase #4 $123.58   12.208%   $138.6666   $138.67   $138.65   $138.70  
  Purchase #5 $231.53   7.617%   $249.1656   $249.17   $249.15   $249.20  
  Purchase #6 $51.28   13.395%   $58.149   $58.15   $58.15   $58.10  
  Purchase #7 $226.41   9.554%   $248.0412   $248.04   $248.05   $248.00  
  7 purchase totals = $1,094.99       $1,209.3121   $1,209.32   $1,209.35   $1,209.30