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 $248.85   10.590%   $275.2032   $275.20   $275.20   $275.20  
  Purchase #2 $189.42   6.622%   $201.9634   $201.96   $201.95   $202.00  
  Purchase #3 $250.27   7.321%   $268.5923   $268.59   $268.60   $268.60  
  Purchase #4 $142.55   8.503%   $154.671   $154.67   $154.65   $154.70  
  Purchase #5 $122.39   5.479%   $129.0957   $129.10   $129.10   $129.10  
  Purchase #6 $161.31   9.316%   $176.3376   $176.34   $176.35   $176.30  
  Purchase #7 $131.40   6.235%   $139.5928   $139.59   $139.60   $139.60  
  7 purchase totals = $1,246.19       $1,345.4560   $1,345.45   $1,345.45   $1,345.50