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 $68.54   12.676%   $77.2281   $77.23   $77.25   $77.20  
  Purchase #2 $131.89   7.299%   $141.5167   $141.52   $141.50   $141.50  
  Purchase #3 $209.96   11.641%   $234.4014   $234.40   $234.40   $234.40  
  Purchase #4 $98.46   9.185%   $107.5036   $107.50   $107.50   $107.50  
  Purchase #5 $212.45   13.785%   $241.7362   $241.74   $241.75   $241.70  
  Purchase #6 $142.32   11.706%   $158.98   $158.98   $159.00   $159.00  
  Purchase #7 $175.56   9.763%   $192.6999   $192.70   $192.70   $192.70  
  7 purchase totals = $1,039.18       $1,154.0659   $1,154.07   $1,154.10   $1,154.00