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 $20.80   4.458%   $21.7273   $21.73   $21.75   $21.70  
  Purchase #2 $89.74   7.430%   $96.4077   $96.41   $96.40   $96.40  
  Purchase #3 $77.55   12.205%   $87.015   $87.02   $87.00   $87.00  
  Purchase #4 $56.65   3.246%   $58.4889   $58.49   $58.50   $58.50  
  Purchase #5 $57.91   9.624%   $63.4833   $63.48   $63.50   $63.50  
  Purchase #6 $50.97   8.847%   $55.4793   $55.48   $55.50   $55.50  
  Purchase #7 $63.87   9.184%   $69.7358   $69.74   $69.75   $69.70  
  7 purchase totals = $417.49       $452.3373   $452.35   $452.40   $452.30