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   9.697%   $65.6866   $65.69   $65.70   $65.70  
  Purchase #2 $141.77   8.180%   $153.3668   $153.37   $153.35   $153.40  
  Purchase #3 $88.64   5.796%   $93.7776   $93.78   $93.80   $93.80  
  Purchase #4 $69.80   7.453%   $75.0022   $75.00   $75.00   $75.00  
  Purchase #5 $216.64   11.349%   $241.2265   $241.23   $241.25   $241.20  
  Purchase #6 $57.60   7.489%   $61.9137   $61.91   $61.90   $61.90  
  Purchase #7 $213.76   5.854%   $226.2735   $226.27   $226.25   $226.30  
  7 purchase totals = $848.09       $917.2469   $917.25   $917.25   $917.30