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 $192.78   5.283%   $202.9646   $202.96   $202.95   $203.00  
  Purchase #2 $61.43   5.491%   $64.8031   $64.80   $64.80   $64.80  
  Purchase #3 $168.95   4.486%   $176.5291   $176.53   $176.55   $176.50  
  Purchase #4 $186.74   4.568%   $195.2703   $195.27   $195.25   $195.30  
  Purchase #5 $83.86   3.436%   $86.7414   $86.74   $86.75   $86.70  
  Purchase #6 $181.52   10.701%   $200.9445   $200.94   $200.95   $200.90  
  Purchase #7 $13.89   11.437%   $15.4786   $15.48   $15.50   $15.50  
  7 purchase totals = $889.17       $942.7316   $942.72   $942.75   $942.70