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 $61.54   12.795%   $69.414   $69.41   $69.40   $69.40  
  Purchase #2 $86.98   11.363%   $96.8635   $96.86   $96.85   $96.90  
  Purchase #3 $198.80   4.626%   $207.9965   $208.00   $208.00   $208.00  
  Purchase #4 $184.95   12.751%   $208.533   $208.53   $208.55   $208.50  
  Purchase #5 $150.41   9.377%   $164.5139   $164.51   $164.50   $164.50  
  Purchase #6 $168.52   5.708%   $178.1391   $178.14   $178.15   $178.10  
  Purchase #7 $184.36   5.633%   $194.745   $194.75   $194.75   $194.70  
  7 purchase totals = $1,035.56       $1,120.2050   $1,120.20   $1,120.20   $1,120.10