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 $213.83   13.782%   $243.3001   $243.30   $243.30   $243.30  
  Purchase #2 $43.63   6.704%   $46.555   $46.56   $46.55   $46.60  
  Purchase #3 $23.70   6.134%   $25.1538   $25.15   $25.15   $25.20  
  Purchase #4 $231.44   6.113%   $245.5879   $245.59   $245.60   $245.60  
  Purchase #5 $151.46   9.227%   $165.4352   $165.44   $165.45   $165.40  
  Purchase #6 $227.49   10.254%   $250.8168   $250.82   $250.80   $250.80  
  Purchase #7 $194.83   6.673%   $207.831   $207.83   $207.85   $207.80  
  7 purchase totals = $1,086.38       $1,184.6798   $1,184.69   $1,184.70   $1,184.70