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 $205.43   10.249%   $226.4845   $226.48   $226.50   $226.50  
  Purchase #2 $31.56   3.795%   $32.7577   $32.76   $32.75   $32.80  
  Purchase #3 $57.35   5.675%   $60.6046   $60.60   $60.60   $60.60  
  Purchase #4 $51.51   8.748%   $56.0161   $56.02   $56.00   $56.00  
  Purchase #5 $51.89   12.384%   $58.3161   $58.32   $58.30   $58.30  
  Purchase #6 $224.57   4.511%   $234.7004   $234.70   $234.70   $234.70  
  Purchase #7 $170.31   8.301%   $184.4474   $184.45   $184.45   $184.40  
  7 purchase totals = $792.62       $853.3268   $853.33   $853.30   $853.30