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 $240.44   11.507%   $268.1074   $268.11   $268.10   $268.10  
  Purchase #2 $67.40   5.827%   $71.3274   $71.33   $71.35   $71.30  
  Purchase #3 $68.68   12.275%   $77.1105   $77.11   $77.10   $77.10  
  Purchase #4 $248.35   4.109%   $258.5547   $258.55   $258.55   $258.60  
  Purchase #5 $20.98   8.208%   $22.702   $22.70   $22.70   $22.70  
  Purchase #6 $203.92   3.362%   $210.7758   $210.78   $210.80   $210.80  
  Purchase #7 $136.52   8.626%   $148.2962   $148.30   $148.30   $148.30  
  7 purchase totals = $986.29       $1,056.8740   $1,056.88   $1,056.90   $1,056.90