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 $219.83   10.577%   $243.0814   $243.08   $243.10   $243.10  
  Purchase #2 $58.62   11.447%   $65.3302   $65.33   $65.35   $65.30  
  Purchase #3 $225.93   7.594%   $243.0871   $243.09   $243.10   $243.10  
  Purchase #4 $229.59   7.446%   $246.6853   $246.69   $246.70   $246.70  
  Purchase #5 $107.68   7.709%   $115.9811   $115.98   $116.00   $116.00  
  Purchase #6 $61.90   6.862%   $66.1476   $66.15   $66.15   $66.10  
  Purchase #7 $26.80   13.166%   $30.3285   $30.33   $30.35   $30.30  
  7 purchase totals = $930.35       $1,010.6412   $1,010.65   $1,010.75   $1,010.60