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 $150.73   8.181%   $163.0612   $163.06   $163.05   $163.10  
  Purchase #2 $77.41   13.655%   $87.9803   $87.98   $88.00   $88.00  
  Purchase #3 $99.97   7.371%   $107.3388   $107.34   $107.35   $107.30  
  Purchase #4 $24.59   11.835%   $27.5002   $27.50   $27.50   $27.50  
  Purchase #5 $250.53   3.656%   $259.6894   $259.69   $259.70   $259.70  
  Purchase #6 $167.85   10.134%   $184.8599   $184.86   $184.85   $184.90  
  Purchase #7 $183.39   5.284%   $193.0803   $193.08   $193.10   $193.10  
  7 purchase totals = $954.47       $1,023.5101   $1,023.51   $1,023.55   $1,023.60