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 $46.72   13.813%   $53.1734   $53.17   $53.15   $53.20  
  Purchase #2 $176.53   8.424%   $191.4009   $191.40   $191.40   $191.40  
  Purchase #3 $122.42   7.811%   $131.9822   $131.98   $132.00   $132.00  
  Purchase #4 $69.27   3.229%   $71.5067   $71.51   $71.50   $71.50  
  Purchase #5 $181.66   7.112%   $194.5797   $194.58   $194.60   $194.60  
  Purchase #6 $30.26   9.122%   $33.0203   $33.02   $33.00   $33.00  
  Purchase #7 $163.38   11.418%   $182.0347   $182.03   $182.05   $182.00  
  7 purchase totals = $790.24       $857.6979   $857.69   $857.70   $857.70