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 $108.33   11.673%   $120.9754   $120.98   $121.00   $121.00  
  Purchase #2 $124.71   13.824%   $141.9499   $141.95   $141.95   $141.90  
  Purchase #3 $24.63   10.110%   $27.1201   $27.12   $27.10   $27.10  
  Purchase #4 $219.39   12.448%   $246.6997   $246.70   $246.70   $246.70  
  Purchase #5 $93.57   4.382%   $97.6702   $97.67   $97.65   $97.70  
  Purchase #6 $228.69   5.738%   $241.8122   $241.81   $241.80   $241.80  
  Purchase #7 $109.69   13.671%   $124.6857   $124.69   $124.70   $124.70  
  7 purchase totals = $909.01       $1,000.9132   $1,000.92   $1,000.90   $1,000.90