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 $32.58   4.426%   $34.022   $34.02   $34.00   $34.00  
  Purchase #2 $234.46   11.720%   $261.9387   $261.94   $261.95   $261.90  
  Purchase #3 $49.59   10.320%   $54.7077   $54.71   $54.70   $54.70  
  Purchase #4 $112.29   8.762%   $122.1288   $122.13   $122.15   $122.10  
  Purchase #5 $31.50   6.180%   $33.4467   $33.45   $33.45   $33.40  
  Purchase #6 $65.78   4.265%   $68.5855   $68.59   $68.60   $68.60  
  Purchase #7 $38.56   12.453%   $43.3619   $43.36   $43.35   $43.40  
  7 purchase totals = $564.76       $618.1913   $618.20   $618.20   $618.10