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 $47.27   13.640%   $53.7176   $53.72   $53.70   $53.70  
  Purchase #2 $192.34   11.574%   $214.6014   $214.60   $214.60   $214.60  
  Purchase #3 $204.93   12.465%   $230.4745   $230.47   $230.45   $230.50  
  Purchase #4 $179.51   4.503%   $187.5933   $187.59   $187.60   $187.60  
  Purchase #5 $55.34   11.340%   $61.6156   $61.62   $61.60   $61.60  
  Purchase #6 $179.68   7.223%   $192.6583   $192.66   $192.65   $192.70  
  Purchase #7 $74.29   6.359%   $79.0141   $79.01   $79.00   $79.00  
  7 purchase totals = $933.36       $1,019.6748   $1,019.67   $1,019.60   $1,019.70