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 $47.96   13.121%   $54.2528   $54.25   $54.25   $54.30  
  Purchase #2 $241.38   12.682%   $271.9918   $271.99   $272.00   $272.00  
  Purchase #3 $58.93   11.832%   $65.9026   $65.90   $65.90   $65.90  
  Purchase #4 $44.83   6.581%   $47.7803   $47.78   $47.80   $47.80  
  Purchase #5 $102.57   3.178%   $105.8297   $105.83   $105.85   $105.80  
  Purchase #6 $68.50   12.551%   $77.0974   $77.10   $77.10   $77.10  
  Purchase #7 $226.75   12.192%   $254.3954   $254.40   $254.40   $254.40  
  7 purchase totals = $790.92       $877.2500   $877.25   $877.30   $877.30