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 $45.28   8.545%   $49.1492   $49.15   $49.15   $49.10  
  Purchase #2 $182.57   7.645%   $196.5275   $196.53   $196.55   $196.50  
  Purchase #3 $235.44   12.575%   $265.0466   $265.05   $265.05   $265.00  
  Purchase #4 $141.76   12.578%   $159.5906   $159.59   $159.60   $159.60  
  Purchase #5 $178.47   10.268%   $196.7953   $196.80   $196.80   $196.80  
  Purchase #6 $153.31   5.499%   $161.7405   $161.74   $161.75   $161.70  
  Purchase #7 $154.65   13.411%   $175.3901   $175.39   $175.40   $175.40  
  7 purchase totals = $1,091.48       $1,204.2398   $1,204.25   $1,204.30   $1,204.10