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 $60.63   11.510%   $67.6085   $67.61   $67.60   $67.60  
  Purchase #2 $127.40   6.106%   $135.179   $135.18   $135.20   $135.20  
  Purchase #3 $22.53   10.121%   $24.8103   $24.81   $24.80   $24.80  
  Purchase #4 $92.80   6.699%   $99.0167   $99.02   $99.00   $99.00  
  Purchase #5 $92.52   3.346%   $95.6157   $95.62   $95.60   $95.60  
  Purchase #6 $241.25   11.392%   $268.7332   $268.73   $268.75   $268.70  
  Purchase #7 $152.96   10.415%   $168.8908   $168.89   $168.90   $168.90  
  7 purchase totals = $790.09       $859.8542   $859.86   $859.85   $859.80