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 $186.66   8.106%   $201.7907   $201.79   $201.80   $201.80  
  Purchase #2 $43.50   12.813%   $49.0737   $49.07   $49.05   $49.10  
  Purchase #3 $116.53   4.735%   $122.0477   $122.05   $122.05   $122.00  
  Purchase #4 $89.31   7.695%   $96.1824   $96.18   $96.20   $96.20  
  Purchase #5 $28.87   8.744%   $31.3944   $31.39   $31.40   $31.40  
  Purchase #6 $188.39   9.657%   $206.5828   $206.58   $206.60   $206.60  
  Purchase #7 $232.87   5.284%   $245.1749   $245.17   $245.15   $245.20  
  7 purchase totals = $886.13       $952.2466   $952.23   $952.25   $952.30