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 $49.59   8.249%   $53.6807   $53.68   $53.70   $53.70  
  Purchase #2 $32.39   12.765%   $36.5246   $36.52   $36.50   $36.50  
  Purchase #3 $172.68   7.490%   $185.6137   $185.61   $185.60   $185.60  
  Purchase #4 $199.86   3.698%   $207.2508   $207.25   $207.25   $207.30  
  Purchase #5 $227.30   6.631%   $242.3723   $242.37   $242.35   $242.40  
  Purchase #6 $215.51   3.214%   $222.4365   $222.44   $222.45   $222.40  
  Purchase #7 $96.74   13.846%   $110.1346   $110.13   $110.15   $110.10  
  7 purchase totals = $994.07       $1,058.0132   $1,058.00   $1,058.00   $1,058.00