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 $186.87   3.461%   $193.3376   $193.34   $193.35   $193.30  
  Purchase #2 $123.37   4.287%   $128.6589   $128.66   $128.65   $128.70  
  Purchase #3 $91.25   6.219%   $96.9248   $96.92   $96.90   $96.90  
  Purchase #4 $202.29   6.547%   $215.5339   $215.53   $215.55   $215.50  
  Purchase #5 $186.27   3.759%   $193.2719   $193.27   $193.25   $193.30  
  Purchase #6 $227.39   6.702%   $242.6297   $242.63   $242.65   $242.60  
  Purchase #7 $67.42   6.249%   $71.6331   $71.63   $71.65   $71.60  
  7 purchase totals = $1,084.86       $1,141.9899   $1,141.98   $1,142.00   $1,141.90