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 $59.88   5.712%   $63.3003   $63.30   $63.30   $63.30  
  Purchase #2 $31.71   11.469%   $35.3468   $35.35   $35.35   $35.30  
  Purchase #3 $100.41   9.760%   $110.21   $110.21   $110.20   $110.20  
  Purchase #4 $106.45   6.631%   $113.5087   $113.51   $113.50   $113.50  
  Purchase #5 $197.28   4.755%   $206.6607   $206.66   $206.65   $206.70  
  Purchase #6 $231.64   11.837%   $259.0592   $259.06   $259.05   $259.10  
  Purchase #7 $144.62   13.780%   $164.5486   $164.55   $164.55   $164.50  
  7 purchase totals = $871.99       $952.6343   $952.64   $952.60   $952.60