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 $211.80   9.633%   $232.2027   $232.20   $232.20   $232.20  
  Purchase #2 $195.51   10.763%   $216.5527   $216.55   $216.55   $216.60  
  Purchase #3 $138.26   4.603%   $144.6241   $144.62   $144.60   $144.60  
  Purchase #4 $91.85   3.487%   $95.0528   $95.05   $95.05   $95.10  
  Purchase #5 $176.75   7.678%   $190.3209   $190.32   $190.30   $190.30  
  Purchase #6 $109.29   12.867%   $123.3523   $123.35   $123.35   $123.40  
  Purchase #7 $60.96   11.220%   $67.7997   $67.80   $67.80   $67.80  
  7 purchase totals = $984.42       $1,069.9052   $1,069.89   $1,069.85   $1,070.00