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 $98.29   5.354%   $103.5524   $103.55   $103.55   $103.60  
  Purchase #2 $233.50   4.455%   $243.9024   $243.90   $243.90   $243.90  
  Purchase #3 $75.77   9.564%   $83.0166   $83.02   $83.00   $83.00  
  Purchase #4 $26.28   7.127%   $28.153   $28.15   $28.15   $28.20  
  Purchase #5 $190.55   11.746%   $212.932   $212.93   $212.95   $212.90  
  Purchase #6 $153.74   9.113%   $167.7503   $167.75   $167.75   $167.80  
  Purchase #7 $185.78   4.233%   $193.6441   $193.64   $193.65   $193.60  
  7 purchase totals = $963.91       $1,032.9508   $1,032.94   $1,032.95   $1,033.00