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 $216.75   8.744%   $235.7026   $235.70   $235.70   $235.70  
  Purchase #2 $144.33   11.291%   $160.6263   $160.63   $160.65   $160.60  
  Purchase #3 $239.95   13.468%   $272.2665   $272.27   $272.25   $272.30  
  Purchase #4 $209.84   13.293%   $237.734   $237.73   $237.75   $237.70  
  Purchase #5 $117.35   3.112%   $121.0019   $121.00   $121.00   $121.00  
  Purchase #6 $146.89   13.721%   $167.0448   $167.04   $167.05   $167.00  
  Purchase #7 $219.31   9.243%   $239.5808   $239.58   $239.60   $239.60  
  7 purchase totals = $1,294.42       $1,433.9569   $1,433.95   $1,434.00   $1,433.90