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 $168.83   5.194%   $177.599   $177.60   $177.60   $177.60  
  Purchase #2 $226.67   13.762%   $257.8643   $257.86   $257.85   $257.90  
  Purchase #3 $124.81   12.135%   $139.9557   $139.96   $139.95   $140.00  
  Purchase #4 $152.95   10.590%   $169.1474   $169.15   $169.15   $169.10  
  Purchase #5 $6.94   9.346%   $7.5886   $7.59   $7.60   $7.60  
  Purchase #6 $96.92   11.173%   $107.7489   $107.75   $107.75   $107.70  
  Purchase #7 $181.85   11.138%   $202.1045   $202.10   $202.10   $202.10  
  7 purchase totals = $958.97       $1,062.0084   $1,062.01   $1,062.00   $1,062.00