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 $58.64   5.297%   $61.7462   $61.75   $61.75   $61.70  
  Purchase #2 $63.36   5.185%   $66.6452   $66.65   $66.65   $66.60  
  Purchase #3 $192.63   9.738%   $211.3883   $211.39   $211.40   $211.40  
  Purchase #4 $35.35   5.470%   $37.2836   $37.28   $37.30   $37.30  
  Purchase #5 $77.69   9.436%   $85.0208   $85.02   $85.00   $85.00  
  Purchase #6 $98.61   8.568%   $107.0589   $107.06   $107.05   $107.10  
  Purchase #7 $248.29   9.559%   $272.024   $272.02   $272.00   $272.00  
  7 purchase totals = $774.57       $841.1670   $841.17   $841.15   $841.10