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 $58.35   5.871%   $61.7757   $61.78   $61.80   $61.80  
  Purchase #2 $15.33   11.848%   $17.1463   $17.15   $17.15   $17.10  
  Purchase #3 $223.76   4.714%   $234.308   $234.31   $234.30   $234.30  
  Purchase #4 $193.89   4.812%   $203.22   $203.22   $203.20   $203.20  
  Purchase #5 $232.93   8.614%   $252.9946   $252.99   $253.00   $253.00  
  Purchase #6 $190.34   8.120%   $205.7956   $205.80   $205.80   $205.80  
  Purchase #7 $78.96   7.730%   $85.0636   $85.06   $85.05   $85.10  
  7 purchase totals = $993.56       $1,060.3038   $1,060.31   $1,060.30   $1,060.30