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 $244.70   9.646%   $268.3038   $268.30   $268.30   $268.30  
  Purchase #2 $125.93   7.851%   $135.8168   $135.82   $135.80   $135.80  
  Purchase #3 $7.26   5.595%   $7.6662   $7.67   $7.65   $7.70  
  Purchase #4 $72.42   13.349%   $82.0873   $82.09   $82.10   $82.10  
  Purchase #5 $218.79   10.218%   $241.146   $241.15   $241.15   $241.10  
  Purchase #6 $52.44   11.511%   $58.4764   $58.48   $58.50   $58.50  
  Purchase #7 $235.61   13.738%   $267.9781   $267.98   $268.00   $268.00  
  7 purchase totals = $957.15       $1,061.4746   $1,061.49   $1,061.50   $1,061.50