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 $57.33   13.143%   $64.8649   $64.86   $64.85   $64.90  
  Purchase #2 $151.98   9.110%   $165.8254   $165.83   $165.85   $165.80  
  Purchase #3 $66.41   7.501%   $71.3914   $71.39   $71.40   $71.40  
  Purchase #4 $155.60   7.321%   $166.9915   $166.99   $167.00   $167.00  
  Purchase #5 $112.74   9.608%   $123.5721   $123.57   $123.55   $123.60  
  Purchase #6 $192.58   4.775%   $201.7757   $201.78   $201.80   $201.80  
  Purchase #7 $236.94   12.320%   $266.131   $266.13   $266.15   $266.10  
  7 purchase totals = $973.58       $1,060.5520   $1,060.55   $1,060.60   $1,060.60