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 $109.61   13.283%   $124.1695   $124.17   $124.15   $124.20  
  Purchase #2 $202.68   11.689%   $226.3713   $226.37   $226.35   $226.40  
  Purchase #3 $49.35   6.651%   $52.6323   $52.63   $52.65   $52.60  
  Purchase #4 $186.64   7.678%   $200.9702   $200.97   $200.95   $201.00  
  Purchase #5 $149.81   10.843%   $166.0539   $166.05   $166.05   $166.10  
  Purchase #6 $191.43   8.138%   $207.0086   $207.01   $207.00   $207.00  
  Purchase #7 $83.65   10.494%   $92.4282   $92.43   $92.45   $92.40  
  7 purchase totals = $973.17       $1,069.6340   $1,069.63   $1,069.60   $1,069.70