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 $56.74   7.287%   $60.8746   $60.87   $60.85   $60.90  
  Purchase #2 $223.45   8.233%   $241.8466   $241.85   $241.85   $241.80  
  Purchase #3 $156.31   7.154%   $167.4924   $167.49   $167.50   $167.50  
  Purchase #4 $60.40   9.443%   $66.1036   $66.10   $66.10   $66.10  
  Purchase #5 $186.51   11.815%   $208.5462   $208.55   $208.55   $208.50  
  Purchase #6 $57.55   9.398%   $62.9585   $62.96   $62.95   $63.00  
  Purchase #7 $72.62   6.165%   $77.097   $77.10   $77.10   $77.10  
  7 purchase totals = $813.58       $884.9189   $884.92   $884.90   $884.90