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 $68.36   3.412%   $70.6924   $70.69   $70.70   $70.70  
  Purchase #2 $163.98   12.646%   $184.7169   $184.72   $184.70   $184.70  
  Purchase #3 $145.49   12.331%   $163.4304   $163.43   $163.45   $163.40  
  Purchase #4 $27.27   4.592%   $28.5222   $28.52   $28.50   $28.50  
  Purchase #5 $74.43   3.277%   $76.8691   $76.87   $76.85   $76.90  
  Purchase #6 $221.81   3.745%   $230.1168   $230.12   $230.10   $230.10  
  Purchase #7 $126.56   11.788%   $141.4789   $141.48   $141.50   $141.50  
  7 purchase totals = $827.90       $895.8267   $895.83   $895.80   $895.80