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 $83.37   10.731%   $92.3164   $92.32   $92.30   $92.30  
  Purchase #2 $37.70   10.319%   $41.5903   $41.59   $41.60   $41.60  
  Purchase #3 $58.79   11.166%   $65.3545   $65.35   $65.35   $65.40  
  Purchase #4 $247.51   7.498%   $266.0683   $266.07   $266.05   $266.10  
  Purchase #5 $17.38   9.373%   $19.009   $19.01   $19.00   $19.00  
  Purchase #6 $113.50   12.474%   $127.658   $127.66   $127.65   $127.70  
  Purchase #7 $13.25   7.382%   $14.2281   $14.23   $14.25   $14.20  
  7 purchase totals = $571.50       $626.2246   $626.23   $626.20   $626.30