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 $47.31   12.441%   $53.1958   $53.20   $53.20   $53.20  
  Purchase #2 $117.94   8.764%   $128.2763   $128.28   $128.30   $128.30  
  Purchase #3 $163.67   4.465%   $170.9779   $170.98   $171.00   $171.00  
  Purchase #4 $187.39   3.418%   $193.795   $193.80   $193.80   $193.80  
  Purchase #5 $35.97   3.611%   $37.2689   $37.27   $37.25   $37.30  
  Purchase #6 $82.88   7.676%   $89.2419   $89.24   $89.25   $89.20  
  Purchase #7 $179.27   12.405%   $201.5084   $201.51   $201.50   $201.50  
  7 purchase totals = $814.43       $874.2642   $874.28   $874.30   $874.30