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 $57.54   6.164%   $61.0868   $61.09   $61.10   $61.10  
  Purchase #2 $42.36   10.802%   $46.9357   $46.94   $46.95   $46.90  
  Purchase #3 $93.29   9.815%   $102.4464   $102.45   $102.45   $102.40  
  Purchase #4 $162.78   8.798%   $177.1014   $177.10   $177.10   $177.10  
  Purchase #5 $163.65   5.294%   $172.3136   $172.31   $172.30   $172.30  
  Purchase #6 $63.65   3.167%   $65.6658   $65.67   $65.65   $65.70  
  Purchase #7 $125.43   7.199%   $134.4597   $134.46   $134.45   $134.50  
  7 purchase totals = $708.70       $760.0094   $760.02   $760.00   $760.00