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 $118.46   11.652%   $132.263   $132.26   $132.25   $132.30  
  Purchase #2 $198.39   11.169%   $220.5482   $220.55   $220.55   $220.50  
  Purchase #3 $21.97   11.470%   $24.49   $24.49   $24.50   $24.50  
  Purchase #4 $23.95   7.267%   $25.6904   $25.69   $25.70   $25.70  
  Purchase #5 $73.77   6.107%   $78.2751   $78.28   $78.30   $78.30  
  Purchase #6 $250.65   6.382%   $266.6465   $266.65   $266.65   $266.60  
  Purchase #7 $235.82   4.712%   $246.9318   $246.93   $246.95   $246.90  
  7 purchase totals = $923.01       $994.8450   $994.85   $994.90   $994.80