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 $156.58   11.398%   $174.427   $174.43   $174.45   $174.40  
  Purchase #2 $32.30   8.205%   $34.9502   $34.95   $34.95   $35.00  
  Purchase #3 $34.79   11.673%   $38.851   $38.85   $38.85   $38.90  
  Purchase #4 $227.27   8.258%   $246.038   $246.04   $246.05   $246.00  
  Purchase #5 $23.42   12.801%   $26.418   $26.42   $26.40   $26.40  
  Purchase #6 $80.42   9.689%   $88.2119   $88.21   $88.20   $88.20  
  Purchase #7 $79.66   10.783%   $88.2497   $88.25   $88.25   $88.20  
  7 purchase totals = $634.44       $697.1458   $697.15   $697.15   $697.10