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 $58.95   12.534%   $66.3388   $66.34   $66.35   $66.30  
  Purchase #2 $95.90   3.187%   $98.9563   $98.96   $98.95   $99.00  
  Purchase #3 $83.66   12.451%   $94.0765   $94.08   $94.10   $94.10  
  Purchase #4 $228.93   13.638%   $260.1515   $260.15   $260.15   $260.20  
  Purchase #5 $180.32   5.391%   $190.0411   $190.04   $190.05   $190.00  
  Purchase #6 $208.90   6.291%   $222.0419   $222.04   $222.05   $222.00  
  Purchase #7 $109.52   10.464%   $120.9802   $120.98   $121.00   $121.00  
  7 purchase totals = $966.18       $1,052.5863   $1,052.59   $1,052.65   $1,052.60