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 $212.49   6.454%   $226.2041   $226.20   $226.20   $226.20  
  Purchase #2 $194.80   7.232%   $208.8879   $208.89   $208.90   $208.90  
  Purchase #3 $108.69   4.822%   $113.931   $113.93   $113.95   $113.90  
  Purchase #4 $96.79   3.587%   $100.2619   $100.26   $100.25   $100.30  
  Purchase #5 $186.52   9.427%   $204.1032   $204.10   $204.10   $204.10  
  Purchase #6 $84.99   13.229%   $96.2333   $96.23   $96.25   $96.20  
  Purchase #7 $152.73   4.239%   $159.2042   $159.20   $159.20   $159.20  
  7 purchase totals = $1,037.01       $1,108.8256   $1,108.81   $1,108.85   $1,108.80