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 $58.71   4.788%   $61.521   $61.52   $61.50   $61.50  
  Purchase #2 $240.45   10.814%   $266.4523   $266.45   $266.45   $266.50  
  Purchase #3 $202.77   8.119%   $219.2329   $219.23   $219.25   $219.20  
  Purchase #4 $148.54   8.692%   $161.4511   $161.45   $161.45   $161.50  
  Purchase #5 $16.87   13.669%   $19.176   $19.18   $19.20   $19.20  
  Purchase #6 $177.29   12.624%   $199.6711   $199.67   $199.65   $199.70  
  Purchase #7 $61.93   9.553%   $67.8462   $67.85   $67.85   $67.80  
  7 purchase totals = $906.56       $995.3506   $995.35   $995.35   $995.40