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 $143.46   5.265%   $151.0132   $151.01   $151.00   $151.00  
  Purchase #2 $160.93   8.442%   $174.5157   $174.52   $174.50   $174.50  
  Purchase #3 $78.90   10.549%   $87.2232   $87.22   $87.20   $87.20  
  Purchase #4 $231.99   8.426%   $251.5375   $251.54   $251.55   $251.50  
  Purchase #5 $52.33   3.707%   $54.2699   $54.27   $54.25   $54.30  
  Purchase #6 $26.96   6.332%   $28.6671   $28.67   $28.65   $28.70  
  Purchase #7 $11.26   6.542%   $11.9966   $12.00   $12.00   $12.00  
  7 purchase totals = $705.83       $759.2232   $759.23   $759.15   $759.20