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 $245.49   9.787%   $269.5161   $269.52   $269.50   $269.50  
  Purchase #2 $132.74   3.729%   $137.6899   $137.69   $137.70   $137.70  
  Purchase #3 $241.61   5.340%   $254.512   $254.51   $254.50   $254.50  
  Purchase #4 $31.35   5.409%   $33.0457   $33.05   $33.05   $33.00  
  Purchase #5 $161.25   9.641%   $176.7961   $176.80   $176.80   $176.80  
  Purchase #6 $61.91   8.168%   $66.9668   $66.97   $66.95   $67.00  
  Purchase #7 $72.35   6.514%   $77.0629   $77.06   $77.05   $77.10  
  7 purchase totals = $946.70       $1,015.5895   $1,015.60   $1,015.55   $1,015.60