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 $60.34   5.741%   $63.8041   $63.80   $63.80   $63.80  
  Purchase #2 $80.45   9.798%   $88.3325   $88.33   $88.35   $88.30  
  Purchase #3 $187.53   7.172%   $200.9797   $200.98   $201.00   $201.00  
  Purchase #4 $130.43   3.458%   $134.9403   $134.94   $134.95   $134.90  
  Purchase #5 $222.82   8.345%   $241.4143   $241.41   $241.40   $241.40  
  Purchase #6 $136.66   13.781%   $155.4931   $155.49   $155.50   $155.50  
  Purchase #7 $105.31   6.698%   $112.3637   $112.36   $112.35   $112.40  
  7 purchase totals = $923.54       $997.3277   $997.31   $997.35   $997.30