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 $153.83   13.288%   $174.2709   $174.27   $174.25   $174.30  
  Purchase #2 $64.37   8.775%   $70.0185   $70.02   $70.00   $70.00  
  Purchase #3 $110.26   12.834%   $124.4108   $124.41   $124.40   $124.40  
  Purchase #4 $145.61   13.256%   $164.9121   $164.91   $164.90   $164.90  
  Purchase #5 $179.71   11.863%   $201.029   $201.03   $201.05   $201.00  
  Purchase #6 $173.50   12.275%   $194.7971   $194.80   $194.80   $194.80  
  Purchase #7 $184.33   3.642%   $191.0433   $191.04   $191.05   $191.00  
  7 purchase totals = $1,011.61       $1,120.4817   $1,120.48   $1,120.45   $1,120.40