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 $220.91   11.360%   $246.0054   $246.01   $246.00   $246.00  
  Purchase #2 $14.95   12.808%   $16.8648   $16.86   $16.85   $16.90  
  Purchase #3 $220.31   11.326%   $245.2623   $245.26   $245.25   $245.30  
  Purchase #4 $120.56   4.613%   $126.1214   $126.12   $126.10   $126.10  
  Purchase #5 $112.90   10.401%   $124.6427   $124.64   $124.65   $124.60  
  Purchase #6 $211.55   10.682%   $234.1478   $234.15   $234.15   $234.10  
  Purchase #7 $43.55   13.257%   $49.3234   $49.32   $49.30   $49.30  
  7 purchase totals = $944.73       $1,042.3678   $1,042.36   $1,042.30   $1,042.30