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 $206.29   6.168%   $219.014   $219.01   $219.00   $219.00  
  Purchase #2 $26.29   9.133%   $28.6911   $28.69   $28.70   $28.70  
  Purchase #3 $70.27   8.292%   $76.0968   $76.10   $76.10   $76.10  
  Purchase #4 $199.48   8.757%   $216.9485   $216.95   $216.95   $216.90  
  Purchase #5 $123.39   11.784%   $137.9303   $137.93   $137.95   $137.90  
  Purchase #6 $145.95   4.711%   $152.8257   $152.83   $152.85   $152.80  
  Purchase #7 $76.80   4.655%   $80.375   $80.38   $80.40   $80.40  
  7 purchase totals = $848.47       $911.8814   $911.89   $911.95   $911.80