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 $241.96   9.852%   $265.7979   $265.80   $265.80   $265.80  
  Purchase #2 $222.28   4.624%   $232.5582   $232.56   $232.55   $232.60  
  Purchase #3 $241.99   5.436%   $255.1446   $255.14   $255.15   $255.10  
  Purchase #4 $38.72   7.687%   $41.6964   $41.70   $41.70   $41.70  
  Purchase #5 $210.36   8.804%   $228.8801   $228.88   $228.90   $228.90  
  Purchase #6 $173.98   7.692%   $187.3625   $187.36   $187.35   $187.40  
  Purchase #7 $219.95   10.488%   $243.0184   $243.02   $243.00   $243.00  
  7 purchase totals = $1,349.24       $1,454.4581   $1,454.46   $1,454.45   $1,454.50