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 $82.31   13.815%   $93.6811   $93.68   $93.70   $93.70  
  Purchase #2 $106.96   7.664%   $115.1574   $115.16   $115.15   $115.20  
  Purchase #3 $130.96   5.461%   $138.1117   $138.11   $138.10   $138.10  
  Purchase #4 $195.91   8.771%   $213.0933   $213.09   $213.10   $213.10  
  Purchase #5 $188.61   9.567%   $206.6543   $206.65   $206.65   $206.70  
  Purchase #6 $96.67   6.684%   $103.1314   $103.13   $103.15   $103.10  
  Purchase #7 $224.35   8.421%   $243.2425   $243.24   $243.25   $243.20  
  7 purchase totals = $1,025.77       $1,113.0717   $1,113.06   $1,113.10   $1,113.10