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 $204.65   11.689%   $228.5715   $228.57   $228.55   $228.60  
  Purchase #2 $137.58   12.592%   $154.9041   $154.90   $154.90   $154.90  
  Purchase #3 $46.91   6.781%   $50.091   $50.09   $50.10   $50.10  
  Purchase #4 $213.39   9.219%   $233.0624   $233.06   $233.05   $233.10  
  Purchase #5 $73.27   11.839%   $81.9444   $81.94   $81.95   $81.90  
  Purchase #6 $220.78   4.438%   $230.5782   $230.58   $230.60   $230.60  
  Purchase #7 $175.63   3.453%   $181.6945   $181.69   $181.70   $181.70  
  7 purchase totals = $1,072.21       $1,160.8461   $1,160.83   $1,160.85   $1,160.90