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 $77.52   6.569%   $82.6123   $82.61   $82.60   $82.60  
  Purchase #2 $200.68   3.298%   $207.2984   $207.30   $207.30   $207.30  
  Purchase #3 $215.47   9.742%   $236.4611   $236.46   $236.45   $236.50  
  Purchase #4 $166.67   10.840%   $184.737   $184.74   $184.75   $184.70  
  Purchase #5 $27.49   12.421%   $30.9045   $30.90   $30.90   $30.90  
  Purchase #6 $226.44   6.742%   $241.7066   $241.71   $241.70   $241.70  
  Purchase #7 $82.62   6.539%   $88.0225   $88.02   $88.00   $88.00  
  7 purchase totals = $996.89       $1,071.7424   $1,071.74   $1,071.70   $1,071.70