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 $24.67   9.586%   $27.0349   $27.03   $27.05   $27.00  
  Purchase #2 $247.49   11.722%   $276.5008   $276.50   $276.50   $276.50  
  Purchase #3 $202.85   13.583%   $230.4031   $230.40   $230.40   $230.40  
  Purchase #4 $93.55   9.384%   $102.3287   $102.33   $102.35   $102.30  
  Purchase #5 $110.42   4.236%   $115.0974   $115.10   $115.10   $115.10  
  Purchase #6 $176.59   5.329%   $186.0005   $186.00   $186.00   $186.00  
  Purchase #7 $213.28   11.280%   $237.338   $237.34   $237.35   $237.30  
  7 purchase totals = $1,068.85       $1,174.7034   $1,174.70   $1,174.75   $1,174.60