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 $57.94   12.373%   $65.1089   $65.11   $65.10   $65.10  
  Purchase #2 $117.28   7.577%   $126.1663   $126.17   $126.15   $126.20  
  Purchase #3 $232.43   8.539%   $252.2772   $252.28   $252.30   $252.30  
  Purchase #4 $139.66   9.709%   $153.2196   $153.22   $153.20   $153.20  
  Purchase #5 $208.27   9.380%   $227.8057   $227.81   $227.80   $227.80  
  Purchase #6 $88.90   6.366%   $94.5594   $94.56   $94.55   $94.60  
  Purchase #7 $131.57   8.321%   $142.5179   $142.52   $142.50   $142.50  
  7 purchase totals = $976.05       $1,061.6550   $1,061.67   $1,061.60   $1,061.70