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 $192.59   10.563%   $212.9333   $212.93   $212.95   $212.90  
  Purchase #2 $234.29   11.688%   $261.6738   $261.67   $261.65   $261.70  
  Purchase #3 $147.94   10.482%   $163.4471   $163.45   $163.45   $163.40  
  Purchase #4 $74.87   11.730%   $83.6523   $83.65   $83.65   $83.70  
  Purchase #5 $34.56   6.473%   $36.7971   $36.80   $36.80   $36.80  
  Purchase #6 $223.38   6.567%   $238.0494   $238.05   $238.05   $238.00  
  Purchase #7 $109.84   7.849%   $118.4613   $118.46   $118.45   $118.50  
  7 purchase totals = $1,017.47       $1,115.0143   $1,115.01   $1,115.00   $1,115.00