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 $61.54   7.705%   $66.2817   $66.28   $66.30   $66.30  
  Purchase #2 $104.68   13.336%   $118.6401   $118.64   $118.65   $118.60  
  Purchase #3 $208.48   5.524%   $219.9964   $220.00   $220.00   $220.00  
  Purchase #4 $196.80   7.423%   $211.4085   $211.41   $211.40   $211.40  
  Purchase #5 $97.82   8.647%   $106.2785   $106.28   $106.30   $106.30  
  Purchase #6 $93.86   5.671%   $99.1828   $99.18   $99.20   $99.20  
  Purchase #7 $146.29   3.717%   $151.7276   $151.73   $151.75   $151.70  
  7 purchase totals = $909.47       $973.5156   $973.52   $973.60   $973.50