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 $195.79   12.226%   $219.7273   $219.73   $219.75   $219.70  
  Purchase #2 $166.48   8.699%   $180.9621   $180.96   $180.95   $181.00  
  Purchase #3 $39.89   10.388%   $44.0338   $44.03   $44.05   $44.00  
  Purchase #4 $140.84   11.118%   $156.4986   $156.50   $156.50   $156.50  
  Purchase #5 $49.42   12.195%   $55.4468   $55.45   $55.45   $55.40  
  Purchase #6 $16.88   8.617%   $18.3345   $18.33   $18.35   $18.30  
  Purchase #7 $177.49   12.743%   $200.1076   $200.11   $200.10   $200.10  
  7 purchase totals = $786.79       $875.1107   $875.11   $875.15   $875.00