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 $52.68   3.481%   $54.5138   $54.51   $54.50   $54.50  
  Purchase #2 $244.29   10.361%   $269.6009   $269.60   $269.60   $269.60  
  Purchase #3 $41.80   6.864%   $44.6692   $44.67   $44.65   $44.70  
  Purchase #4 $135.49   6.399%   $144.16   $144.16   $144.15   $144.20  
  Purchase #5 $194.90   13.713%   $221.6266   $221.63   $221.65   $221.60  
  Purchase #6 $61.65   6.217%   $65.4828   $65.48   $65.50   $65.50  
  Purchase #7 $173.80   7.363%   $186.5969   $186.60   $186.60   $186.60  
  7 purchase totals = $904.61       $986.6502   $986.65   $986.65   $986.70