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 $41.86   9.320%   $45.7614   $45.76   $45.75   $45.80  
  Purchase #2 $211.70   5.492%   $223.3266   $223.33   $223.35   $223.30  
  Purchase #3 $248.43   9.772%   $272.7066   $272.71   $272.70   $272.70  
  Purchase #4 $147.80   10.512%   $163.3367   $163.34   $163.35   $163.30  
  Purchase #5 $96.56   13.131%   $109.2393   $109.24   $109.25   $109.20  
  Purchase #6 $53.86   13.290%   $61.018   $61.02   $61.00   $61.00  
  Purchase #7 $24.71   4.649%   $25.8588   $25.86   $25.85   $25.90  
  7 purchase totals = $824.92       $901.2474   $901.26   $901.25   $901.20