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 $154.53   13.268%   $175.033   $175.03   $175.05   $175.00  
  Purchase #2 $245.75   9.497%   $269.0889   $269.09   $269.10   $269.10  
  Purchase #3 $16.59   12.411%   $18.649   $18.65   $18.65   $18.60  
  Purchase #4 $214.99   7.158%   $230.379   $230.38   $230.40   $230.40  
  Purchase #5 $129.63   10.828%   $143.6663   $143.67   $143.65   $143.70  
  Purchase #6 $66.85   10.424%   $73.8184   $73.82   $73.80   $73.80  
  Purchase #7 $101.81   8.179%   $110.137   $110.14   $110.15   $110.10  
  7 purchase totals = $930.15       $1,020.7716   $1,020.78   $1,020.80   $1,020.70