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 $23.59   13.721%   $26.8268   $26.83   $26.85   $26.80  
  Purchase #2 $131.52   9.415%   $143.9026   $143.90   $143.90   $143.90  
  Purchase #3 $221.83   9.824%   $243.6226   $243.62   $243.60   $243.60  
  Purchase #4 $236.45   8.159%   $255.742   $255.74   $255.75   $255.70  
  Purchase #5 $61.99   4.858%   $65.0015   $65.00   $65.00   $65.00  
  Purchase #6 $111.97   7.458%   $120.3207   $120.32   $120.30   $120.30  
  Purchase #7 $146.66   4.156%   $152.7552   $152.76   $152.75   $152.80  
  7 purchase totals = $934.01       $1,008.1714   $1,008.17   $1,008.15   $1,008.10