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 $82.95   12.596%   $93.3984   $93.40   $93.40   $93.40  
  Purchase #2 $95.43   4.449%   $99.6757   $99.68   $99.70   $99.70  
  Purchase #3 $189.81   5.488%   $200.2268   $200.23   $200.25   $200.20  
  Purchase #4 $79.45   8.355%   $86.088   $86.09   $86.10   $86.10  
  Purchase #5 $153.45   3.303%   $158.5185   $158.52   $158.50   $158.50  
  Purchase #6 $166.85   12.578%   $187.8364   $187.84   $187.85   $187.80  
  Purchase #7 $45.68   11.623%   $50.9894   $50.99   $51.00   $51.00  
  7 purchase totals = $813.62       $876.7332   $876.75   $876.80   $876.70