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 $174.83   6.692%   $186.5296   $186.53   $186.55   $186.50  
  Purchase #2 $250.99   6.716%   $267.8465   $267.85   $267.85   $267.80  
  Purchase #3 $123.39   6.421%   $131.3129   $131.31   $131.30   $131.30  
  Purchase #4 $156.28   10.444%   $172.6019   $172.60   $172.60   $172.60  
  Purchase #5 $53.73   5.275%   $56.5643   $56.56   $56.55   $56.60  
  Purchase #6 $24.71   6.694%   $26.3641   $26.36   $26.35   $26.40  
  Purchase #7 $53.93   11.770%   $60.2776   $60.28   $60.30   $60.30  
  7 purchase totals = $837.86       $901.4969   $901.49   $901.50   $901.50