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 $85.93   7.547%   $92.4151   $92.42   $92.40   $92.40  
  Purchase #2 $187.44   13.608%   $212.9468   $212.95   $212.95   $212.90  
  Purchase #3 $54.54   6.263%   $57.9558   $57.96   $57.95   $58.00  
  Purchase #4 $222.75   13.208%   $252.1708   $252.17   $252.15   $252.20  
  Purchase #5 $90.85   3.107%   $93.6727   $93.67   $93.65   $93.70  
  Purchase #6 $110.48   4.278%   $115.2063   $115.21   $115.20   $115.20  
  Purchase #7 $153.98   11.456%   $171.6199   $171.62   $171.60   $171.60  
  7 purchase totals = $905.97       $995.9874   $996.00   $995.90   $996.00