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 $165.60   11.430%   $184.5281   $184.53   $184.55   $184.50  
  Purchase #2 $111.67   8.274%   $120.9096   $120.91   $120.90   $120.90  
  Purchase #3 $110.98   9.467%   $121.4865   $121.49   $121.50   $121.50  
  Purchase #4 $233.99   8.862%   $254.7262   $254.73   $254.75   $254.70  
  Purchase #5 $193.47   4.312%   $201.8124   $201.81   $201.80   $201.80  
  Purchase #6 $141.82   4.148%   $147.7027   $147.70   $147.70   $147.70  
  Purchase #7 $24.73   8.847%   $26.9179   $26.92   $26.90   $26.90  
  7 purchase totals = $982.26       $1,058.0834   $1,058.09   $1,058.10   $1,058.00