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 $213.98   13.414%   $242.6833   $242.68   $242.70   $242.70  
  Purchase #2 $147.61   4.347%   $154.0266   $154.03   $154.05   $154.00  
  Purchase #3 $230.66   6.821%   $246.3933   $246.39   $246.40   $246.40  
  Purchase #4 $65.48   4.228%   $68.2485   $68.25   $68.25   $68.20  
  Purchase #5 $209.93   11.718%   $234.5296   $234.53   $234.55   $234.50  
  Purchase #6 $199.80   12.736%   $225.2465   $225.25   $225.25   $225.20  
  Purchase #7 $158.93   4.864%   $166.6604   $166.66   $166.65   $166.70  
  7 purchase totals = $1,226.39       $1,337.7882   $1,337.79   $1,337.85   $1,337.70