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 $211.51   4.343%   $220.6959   $220.70   $220.70   $220.70  
  Purchase #2 $225.64   11.799%   $252.2633   $252.26   $252.25   $252.30  
  Purchase #3 $216.31   10.615%   $239.2713   $239.27   $239.25   $239.30  
  Purchase #4 $231.86   10.409%   $255.9943   $255.99   $256.00   $256.00  
  Purchase #5 $143.74   12.210%   $161.2907   $161.29   $161.30   $161.30  
  Purchase #6 $90.78   10.509%   $100.3201   $100.32   $100.30   $100.30  
  Purchase #7 $35.77   9.559%   $39.1893   $39.19   $39.20   $39.20  
  7 purchase totals = $1,155.61       $1,269.0249   $1,269.02   $1,269.00   $1,269.10