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 $84.80   9.398%   $92.7695   $92.77   $92.75   $92.80  
  Purchase #2 $158.55   13.249%   $179.5563   $179.56   $179.55   $179.60  
  Purchase #3 $211.91   3.236%   $218.7674   $218.77   $218.75   $218.80  
  Purchase #4 $145.48   13.381%   $164.9467   $164.95   $164.95   $164.90  
  Purchase #5 $95.31   9.223%   $104.1004   $104.10   $104.10   $104.10  
  Purchase #6 $23.77   7.183%   $25.4774   $25.48   $25.50   $25.50  
  Purchase #7 $115.73   6.599%   $123.367   $123.37   $123.35   $123.40  
  7 purchase totals = $835.55       $908.9847   $909.00   $908.95   $909.10