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 $57.74   13.873%   $65.7503   $65.75   $65.75   $65.80  
  Purchase #2 $224.36   11.483%   $250.1233   $250.12   $250.10   $250.10  
  Purchase #3 $121.38   10.844%   $134.5424   $134.54   $134.55   $134.50  
  Purchase #4 $106.34   13.699%   $120.9075   $120.91   $120.90   $120.90  
  Purchase #5 $110.35   12.642%   $124.3004   $124.30   $124.30   $124.30  
  Purchase #6 $173.35   4.487%   $181.1282   $181.13   $181.15   $181.10  
  Purchase #7 $232.48   5.845%   $246.0685   $246.07   $246.05   $246.10  
  7 purchase totals = $1,026.00       $1,122.8206   $1,122.82   $1,122.80   $1,122.80