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 $186.37   10.525%   $205.9854   $205.99   $206.00   $206.00  
  Purchase #2 $150.28   7.692%   $161.8395   $161.84   $161.85   $161.80  
  Purchase #3 $53.82   4.372%   $56.173   $56.17   $56.15   $56.20  
  Purchase #4 $228.84   13.446%   $259.6098   $259.61   $259.60   $259.60  
  Purchase #5 $123.96   11.433%   $138.1323   $138.13   $138.15   $138.10  
  Purchase #6 $191.79   7.312%   $205.8137   $205.81   $205.80   $205.80  
  Purchase #7 $53.58   10.873%   $59.4058   $59.41   $59.40   $59.40  
  7 purchase totals = $988.64       $1,086.9595   $1,086.96   $1,086.95   $1,086.90