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 $198.46   13.678%   $225.6054   $225.61   $225.60   $225.60  
  Purchase #2 $56.71   10.355%   $62.5823   $62.58   $62.60   $62.60  
  Purchase #3 $234.77   6.687%   $250.4691   $250.47   $250.45   $250.50  
  Purchase #4 $68.31   8.445%   $74.0788   $74.08   $74.10   $74.10  
  Purchase #5 $139.71   5.290%   $147.1007   $147.10   $147.10   $147.10  
  Purchase #6 $42.66   7.534%   $45.874   $45.87   $45.85   $45.90  
  Purchase #7 $189.97   8.771%   $206.6323   $206.63   $206.65   $206.60  
  7 purchase totals = $930.59       $1,012.3426   $1,012.34   $1,012.35   $1,012.40