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 $53.39   8.563%   $57.9618   $57.96   $57.95   $58.00  
  Purchase #2 $78.30   12.356%   $87.9747   $87.97   $87.95   $88.00  
  Purchase #3 $9.45   3.496%   $9.7804   $9.78   $9.80   $9.80  
  Purchase #4 $188.91   8.855%   $205.638   $205.64   $205.65   $205.60  
  Purchase #5 $80.87   4.273%   $84.3256   $84.33   $84.35   $84.30  
  Purchase #6 $12.90   5.507%   $13.6104   $13.61   $13.60   $13.60  
  Purchase #7 $203.70   5.677%   $215.264   $215.26   $215.25   $215.30  
  7 purchase totals = $627.52       $674.5549   $674.55   $674.55   $674.60