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 $143.66   6.558%   $153.0812   $153.08   $153.10   $153.10  
  Purchase #2 $53.99   12.323%   $60.6432   $60.64   $60.65   $60.60  
  Purchase #3 $21.43   9.682%   $23.5049   $23.50   $23.50   $23.50  
  Purchase #4 $166.34   4.186%   $173.303   $173.30   $173.30   $173.30  
  Purchase #5 $196.56   11.529%   $219.2214   $219.22   $219.20   $219.20  
  Purchase #6 $93.26   3.234%   $96.276   $96.28   $96.30   $96.30  
  Purchase #7 $155.33   10.343%   $171.3958   $171.40   $171.40   $171.40  
  7 purchase totals = $830.57       $897.4255   $897.42   $897.45   $897.40