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 $246.53   5.648%   $260.454   $260.45   $260.45   $260.50  
  Purchase #2 $87.88   12.167%   $98.5724   $98.57   $98.55   $98.60  
  Purchase #3 $81.73   12.424%   $91.8841   $91.88   $91.90   $91.90  
  Purchase #4 $77.88   5.214%   $81.9407   $81.94   $81.95   $81.90  
  Purchase #5 $223.30   5.382%   $235.318   $235.32   $235.30   $235.30  
  Purchase #6 $179.81   12.779%   $202.7879   $202.79   $202.80   $202.80  
  Purchase #7 $25.87   4.770%   $27.104   $27.10   $27.10   $27.10  
  7 purchase totals = $923.00       $998.0611   $998.05   $998.05   $998.10