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 $46.69   12.657%   $52.5996   $52.60   $52.60   $52.60  
  Purchase #2 $167.34   9.333%   $182.9578   $182.96   $182.95   $183.00  
  Purchase #3 $13.42   11.599%   $14.9766   $14.98   $15.00   $15.00  
  Purchase #4 $5.86   5.263%   $6.1684   $6.17   $6.15   $6.20  
  Purchase #5 $247.46   3.457%   $256.0147   $256.01   $256.00   $256.00  
  Purchase #6 $83.74   4.137%   $87.2043   $87.20   $87.20   $87.20  
  Purchase #7 $88.51   6.308%   $94.0932   $94.09   $94.10   $94.10  
  7 purchase totals = $653.02       $694.0146   $694.01   $694.00   $694.10