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 $212.88   13.577%   $241.7827   $241.78   $241.80   $241.80  
  Purchase #2 $59.82   8.153%   $64.6971   $64.70   $64.70   $64.70  
  Purchase #3 $171.77   7.220%   $184.1718   $184.17   $184.15   $184.20  
  Purchase #4 $159.66   3.177%   $164.7324   $164.73   $164.75   $164.70  
  Purchase #5 $24.81   10.328%   $27.3724   $27.37   $27.35   $27.40  
  Purchase #6 $140.81   4.608%   $147.2985   $147.30   $147.30   $147.30  
  Purchase #7 $221.59   3.121%   $228.5058   $228.51   $228.50   $228.50  
  7 purchase totals = $991.34       $1,058.5607   $1,058.56   $1,058.55   $1,058.60