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 $55.88   13.774%   $63.5769   $63.58   $63.60   $63.60  
  Purchase #2 $213.44   6.194%   $226.6605   $226.66   $226.65   $226.70  
  Purchase #3 $160.67   13.113%   $181.7387   $181.74   $181.75   $181.70  
  Purchase #4 $234.69   5.148%   $246.7718   $246.77   $246.75   $246.80  
  Purchase #5 $120.59   5.641%   $127.3925   $127.39   $127.40   $127.40  
  Purchase #6 $195.41   6.318%   $207.756   $207.76   $207.75   $207.80  
  Purchase #7 $60.58   6.154%   $64.3081   $64.31   $64.30   $64.30  
  7 purchase totals = $1,041.26       $1,118.2045   $1,118.21   $1,118.20   $1,118.30