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 $194.38   13.450%   $220.5241   $220.52   $220.50   $220.50  
  Purchase #2 $173.77   3.260%   $179.4349   $179.43   $179.45   $179.40  
  Purchase #3 $8.34   7.676%   $8.9802   $8.98   $9.00   $9.00  
  Purchase #4 $102.52   8.533%   $111.268   $111.27   $111.25   $111.30  
  Purchase #5 $232.63   13.365%   $263.721   $263.72   $263.70   $263.70  
  Purchase #6 $106.57   8.150%   $115.2555   $115.26   $115.25   $115.30  
  Purchase #7 $33.96   9.149%   $37.067   $37.07   $37.05   $37.10  
  7 purchase totals = $852.17       $936.2507   $936.25   $936.20   $936.30