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 $248.57   5.536%   $262.3308   $262.33   $262.35   $262.30  
  Purchase #2 $56.32   13.720%   $64.0471   $64.05   $64.05   $64.00  
  Purchase #3 $46.34   8.277%   $50.1756   $50.18   $50.20   $50.20  
  Purchase #4 $54.74   8.328%   $59.2987   $59.30   $59.30   $59.30  
  Purchase #5 $121.45   7.623%   $130.7081   $130.71   $130.70   $130.70  
  Purchase #6 $242.80   13.180%   $274.801   $274.80   $274.80   $274.80  
  Purchase #7 $199.54   9.792%   $219.079   $219.08   $219.10   $219.10  
  7 purchase totals = $969.76       $1,060.4403   $1,060.45   $1,060.50   $1,060.40