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 $38.47   12.147%   $43.143   $43.14   $43.15   $43.10  
  Purchase #2 $103.34   13.391%   $117.1783   $117.18   $117.20   $117.20  
  Purchase #3 $174.87   11.390%   $194.7877   $194.79   $194.80   $194.80  
  Purchase #4 $98.41   4.623%   $102.9595   $102.96   $102.95   $103.00  
  Purchase #5 $212.65   4.255%   $221.6983   $221.70   $221.70   $221.70  
  Purchase #6 $236.58   4.282%   $246.7104   $246.71   $246.70   $246.70  
  Purchase #7 $63.70   7.172%   $68.2686   $68.27   $68.25   $68.30  
  7 purchase totals = $928.02       $994.7458   $994.75   $994.75   $994.80