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 $62.38   3.529%   $64.5814   $64.58   $64.60   $64.60  
  Purchase #2 $207.30   9.358%   $226.6991   $226.70   $226.70   $226.70  
  Purchase #3 $116.89   8.618%   $126.9636   $126.96   $126.95   $127.00  
  Purchase #4 $41.97   4.551%   $43.8801   $43.88   $43.90   $43.90  
  Purchase #5 $44.46   9.434%   $48.6544   $48.65   $48.65   $48.70  
  Purchase #6 $99.27   5.702%   $104.9304   $104.93   $104.95   $104.90  
  Purchase #7 $84.45   12.547%   $95.0459   $95.05   $95.05   $95.00  
  7 purchase totals = $656.72       $710.7549   $710.75   $710.80   $710.80