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 $232.49   10.787%   $257.5687   $257.57   $257.55   $257.60  
  Purchase #2 $150.67   11.191%   $167.5315   $167.53   $167.55   $167.50  
  Purchase #3 $203.90   10.259%   $224.8181   $224.82   $224.80   $224.80  
  Purchase #4 $236.71   10.442%   $261.4273   $261.43   $261.45   $261.40  
  Purchase #5 $140.83   3.498%   $145.7562   $145.76   $145.75   $145.80  
  Purchase #6 $60.44   7.593%   $65.0292   $65.03   $65.05   $65.00  
  Purchase #7 $62.68   11.576%   $69.9358   $69.94   $69.95   $69.90  
  7 purchase totals = $1,087.72       $1,192.0668   $1,192.08   $1,192.10   $1,192.00