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 $55.77   5.743%   $58.9729   $58.97   $58.95   $59.00  
  Purchase #2 $106.43   13.871%   $121.1929   $121.19   $121.20   $121.20  
  Purchase #3 $149.68   10.339%   $165.1554   $165.16   $165.15   $165.20  
  Purchase #4 $175.62   9.704%   $192.6622   $192.66   $192.65   $192.70  
  Purchase #5 $141.75   13.257%   $160.5418   $160.54   $160.55   $160.50  
  Purchase #6 $24.36   3.625%   $25.2431   $25.24   $25.25   $25.20  
  Purchase #7 $192.29   10.273%   $212.044   $212.04   $212.05   $212.00  
  7 purchase totals = $845.90       $935.8123   $935.80   $935.80   $935.80