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 $78.72   5.830%   $83.3094   $83.31   $83.30   $83.30  
  Purchase #2 $226.87   8.400%   $245.9271   $245.93   $245.95   $245.90  
  Purchase #3 $230.42   12.428%   $259.0566   $259.06   $259.05   $259.10  
  Purchase #4 $125.97   8.492%   $136.6674   $136.67   $136.65   $136.70  
  Purchase #5 $138.82   11.136%   $154.279   $154.28   $154.30   $154.30  
  Purchase #6 $187.67   3.151%   $193.5835   $193.58   $193.60   $193.60  
  Purchase #7 $202.88   9.639%   $222.4356   $222.44   $222.45   $222.40  
  7 purchase totals = $1,191.35       $1,295.2586   $1,295.27   $1,295.30   $1,295.30