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 $111.96   13.214%   $126.7544   $126.75   $126.75   $126.80  
  Purchase #2 $144.58   12.691%   $162.9286   $162.93   $162.95   $162.90  
  Purchase #3 $199.47   12.321%   $224.0467   $224.05   $224.05   $224.00  
  Purchase #4 $61.55   7.661%   $66.2653   $66.27   $66.25   $66.30  
  Purchase #5 $100.89   12.762%   $113.7656   $113.77   $113.75   $113.80  
  Purchase #6 $227.52   9.584%   $249.3255   $249.33   $249.35   $249.30  
  Purchase #7 $70.56   6.234%   $74.9587   $74.96   $74.95   $75.00  
  7 purchase totals = $916.53       $1,018.0448   $1,018.06   $1,018.05   $1,018.10