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 $111.85   8.357%   $121.1973   $121.20   $121.20   $121.20  
  Purchase #2 $163.78   6.634%   $174.6452   $174.65   $174.65   $174.60  
  Purchase #3 $28.67   8.163%   $31.0103   $31.01   $31.00   $31.00  
  Purchase #4 $69.30   10.721%   $76.7297   $76.73   $76.75   $76.70  
  Purchase #5 $246.30   7.149%   $263.908   $263.91   $263.90   $263.90  
  Purchase #6 $187.93   8.696%   $204.2724   $204.27   $204.25   $204.30  
  Purchase #7 $116.64   11.338%   $129.8646   $129.86   $129.85   $129.90  
  7 purchase totals = $924.47       $1,001.6275   $1,001.63   $1,001.60   $1,001.60