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 $68.37   12.531%   $76.9374   $76.94   $76.95   $76.90  
  Purchase #2 $238.67   5.194%   $251.0665   $251.07   $251.05   $251.10  
  Purchase #3 $50.52   8.853%   $54.9925   $54.99   $55.00   $55.00  
  Purchase #4 $149.40   3.608%   $154.7904   $154.79   $154.80   $154.80  
  Purchase #5 $202.86   11.394%   $225.9739   $225.97   $225.95   $226.00  
  Purchase #6 $134.62   6.286%   $143.0822   $143.08   $143.10   $143.10  
  Purchase #7 $62.62   5.478%   $66.0503   $66.05   $66.05   $66.10  
  7 purchase totals = $907.06       $972.8932   $972.89   $972.90   $973.00