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 $41.98   5.773%   $44.4035   $44.40   $44.40   $44.40  
  Purchase #2 $243.31   5.716%   $257.2176   $257.22   $257.20   $257.20  
  Purchase #3 $172.35   4.241%   $179.6594   $179.66   $179.65   $179.70  
  Purchase #4 $155.60   7.793%   $167.7259   $167.73   $167.75   $167.70  
  Purchase #5 $46.85   13.475%   $53.163   $53.16   $53.15   $53.20  
  Purchase #6 $136.75   10.732%   $151.426   $151.43   $151.45   $151.40  
  Purchase #7 $228.35   3.704%   $236.8081   $236.81   $236.80   $236.80  
  7 purchase totals = $1,025.19       $1,090.4035   $1,090.41   $1,090.40   $1,090.40