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 $227.86   11.373%   $253.7745   $253.77   $253.75   $253.80  
  Purchase #2 $43.78   7.341%   $46.9939   $46.99   $47.00   $47.00  
  Purchase #3 $194.89   9.281%   $212.9777   $212.98   $213.00   $213.00  
  Purchase #4 $100.98   11.194%   $112.2837   $112.28   $112.30   $112.30  
  Purchase #5 $208.82   11.212%   $232.2329   $232.23   $232.25   $232.20  
  Purchase #6 $126.44   9.645%   $138.6351   $138.64   $138.65   $138.60  
  Purchase #7 $16.37   4.309%   $17.0754   $17.08   $17.10   $17.10  
  7 purchase totals = $919.14       $1,013.9732   $1,013.97   $1,014.05   $1,014.00