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 $110.32   11.604%   $123.1215   $123.12   $123.10   $123.10  
  Purchase #2 $53.83   5.132%   $56.5926   $56.59   $56.60   $56.60  
  Purchase #3 $104.34   9.853%   $114.6206   $114.62   $114.60   $114.60  
  Purchase #4 $246.55   12.303%   $276.883   $276.88   $276.90   $276.90  
  Purchase #5 $68.45   9.300%   $74.8159   $74.82   $74.80   $74.80  
  Purchase #6 $24.34   6.218%   $25.8535   $25.85   $25.85   $25.90  
  Purchase #7 $210.92   9.286%   $230.506   $230.51   $230.50   $230.50  
  7 purchase totals = $818.75       $902.3931   $902.39   $902.35   $902.40