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 $65.62   11.376%   $73.0849   $73.08   $73.10   $73.10  
  Purchase #2 $165.82   8.520%   $179.9479   $179.95   $179.95   $179.90  
  Purchase #3 $221.30   9.798%   $242.983   $242.98   $243.00   $243.00  
  Purchase #4 $58.63   5.274%   $61.7221   $61.72   $61.70   $61.70  
  Purchase #5 $120.32   8.601%   $130.6687   $130.67   $130.65   $130.70  
  Purchase #6 $20.25   13.536%   $22.991   $22.99   $23.00   $23.00  
  Purchase #7 $217.34   11.430%   $242.182   $242.18   $242.20   $242.20  
  7 purchase totals = $869.28       $953.5796   $953.57   $953.60   $953.60