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 $239.67   5.158%   $252.0322   $252.03   $252.05   $252.00  
  Purchase #2 $146.51   4.651%   $153.3242   $153.32   $153.30   $153.30  
  Purchase #3 $153.56   12.702%   $173.0652   $173.07   $173.05   $173.10  
  Purchase #4 $236.43   7.417%   $253.966   $253.97   $253.95   $254.00  
  Purchase #5 $226.28   9.669%   $248.159   $248.16   $248.15   $248.20  
  Purchase #6 $178.49   12.636%   $201.044   $201.04   $201.05   $201.00  
  Purchase #7 $65.50   9.427%   $71.6747   $71.67   $71.65   $71.70  
  7 purchase totals = $1,246.44       $1,353.2653   $1,353.26   $1,353.20   $1,353.30