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 $56.32   12.669%   $63.4552   $63.46   $63.45   $63.50  
  Purchase #2 $128.46   4.836%   $134.6723   $134.67   $134.65   $134.70  
  Purchase #3 $138.68   10.540%   $153.2969   $153.30   $153.30   $153.30  
  Purchase #4 $231.83   6.656%   $247.2606   $247.26   $247.25   $247.30  
  Purchase #5 $238.94   6.693%   $254.9323   $254.93   $254.95   $254.90  
  Purchase #6 $96.80   9.742%   $106.2303   $106.23   $106.25   $106.20  
  Purchase #7 $34.77   3.348%   $35.9341   $35.93   $35.95   $35.90  
  7 purchase totals = $925.80       $995.7817   $995.78   $995.80   $995.80