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 $243.25   12.648%   $274.0163   $274.02   $274.00   $274.00  
  Purchase #2 $171.65   11.111%   $190.722   $190.72   $190.70   $190.70  
  Purchase #3 $28.64   3.515%   $29.6467   $29.65   $29.65   $29.60  
  Purchase #4 $202.68   3.770%   $210.321   $210.32   $210.30   $210.30  
  Purchase #5 $71.64   12.493%   $80.59   $80.59   $80.60   $80.60  
  Purchase #6 $142.60   9.119%   $155.6037   $155.60   $155.60   $155.60  
  Purchase #7 $215.53   11.479%   $240.2707   $240.27   $240.25   $240.30  
  7 purchase totals = $1,075.99       $1,181.1704   $1,181.17   $1,181.10   $1,181.10