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 $59.56   9.299%   $65.0985   $65.10   $65.10   $65.10  
  Purchase #2 $248.91   10.485%   $275.0082   $275.01   $275.00   $275.00  
  Purchase #3 $61.74   13.146%   $69.8563   $69.86   $69.85   $69.90  
  Purchase #4 $49.54   6.115%   $52.5694   $52.57   $52.55   $52.60  
  Purchase #5 $184.91   10.141%   $203.6617   $203.66   $203.65   $203.70  
  Purchase #6 $141.65   10.692%   $156.7952   $156.80   $156.80   $156.80  
  Purchase #7 $206.86   10.699%   $228.992   $228.99   $229.00   $229.00  
  7 purchase totals = $953.17       $1,051.9813   $1,051.99   $1,051.95   $1,052.10