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 $241.33   11.765%   $269.7225   $269.72   $269.70   $269.70  
  Purchase #2 $226.65   3.356%   $234.2564   $234.26   $234.25   $234.30  
  Purchase #3 $27.41   4.415%   $28.6202   $28.62   $28.60   $28.60  
  Purchase #4 $181.91   10.774%   $201.509   $201.51   $201.50   $201.50  
  Purchase #5 $190.49   6.229%   $202.3556   $202.36   $202.35   $202.40  
  Purchase #6 $78.57   8.264%   $85.063   $85.06   $85.05   $85.10  
  Purchase #7 $184.39   5.633%   $194.7767   $194.78   $194.80   $194.80  
  7 purchase totals = $1,130.75       $1,216.3034   $1,216.31   $1,216.25   $1,216.40