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 $210.30   11.798%   $235.1112   $235.11   $235.10   $235.10  
  Purchase #2 $55.26   13.369%   $62.6477   $62.65   $62.65   $62.60  
  Purchase #3 $209.74   9.272%   $229.1871   $229.19   $229.20   $229.20  
  Purchase #4 $203.85   7.154%   $218.4334   $218.43   $218.45   $218.40  
  Purchase #5 $120.98   3.221%   $124.8768   $124.88   $124.90   $124.90  
  Purchase #6 $54.44   8.724%   $59.1893   $59.19   $59.20   $59.20  
  Purchase #7 $109.60   3.258%   $113.1708   $113.17   $113.15   $113.20  
  7 purchase totals = $964.17       $1,042.6163   $1,042.62   $1,042.65   $1,042.60