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 $126.29   10.621%   $139.7033   $139.70   $139.70   $139.70  
  Purchase #2 $13.63   6.581%   $14.527   $14.53   $14.55   $14.50  
  Purchase #3 $84.43   12.436%   $94.9297   $94.93   $94.95   $94.90  
  Purchase #4 $66.29   8.477%   $71.9094   $71.91   $71.90   $71.90  
  Purchase #5 $118.63   5.768%   $125.4726   $125.47   $125.45   $125.50  
  Purchase #6 $65.56   13.739%   $74.5673   $74.57   $74.55   $74.60  
  Purchase #7 $224.52   7.340%   $240.9998   $241.00   $241.00   $241.00  
  7 purchase totals = $699.35       $762.1091   $762.11   $762.10   $762.10