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 $63.33   11.270%   $70.4673   $70.47   $70.45   $70.50  
  Purchase #2 $147.31   3.564%   $152.5601   $152.56   $152.55   $152.60  
  Purchase #3 $222.65   4.402%   $232.4511   $232.45   $232.45   $232.50  
  Purchase #4 $34.91   4.572%   $36.5061   $36.51   $36.50   $36.50  
  Purchase #5 $221.26   3.619%   $229.2674   $229.27   $229.25   $229.30  
  Purchase #6 $166.25   12.292%   $186.6855   $186.69   $186.70   $186.70  
  Purchase #7 $113.48   10.643%   $125.5577   $125.56   $125.55   $125.60  
  7 purchase totals = $969.19       $1,033.4952   $1,033.51   $1,033.45   $1,033.70