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 $48.85   3.260%   $50.4425   $50.44   $50.45   $50.40  
  Purchase #2 $179.50   13.608%   $203.9264   $203.93   $203.95   $203.90  
  Purchase #3 $245.43   13.548%   $278.6809   $278.68   $278.70   $278.70  
  Purchase #4 $49.92   13.676%   $56.7471   $56.75   $56.75   $56.70  
  Purchase #5 $166.68   10.726%   $184.5581   $184.56   $184.55   $184.60  
  Purchase #6 $210.57   3.213%   $217.3356   $217.34   $217.35   $217.30  
  Purchase #7 $52.26   3.718%   $54.203   $54.20   $54.20   $54.20  
  7 purchase totals = $953.21       $1,045.8936   $1,045.90   $1,045.95   $1,045.80