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 $33.67   11.506%   $37.5441   $37.54   $37.55   $37.50  
  Purchase #2 $147.89   3.838%   $153.566   $153.57   $153.55   $153.60  
  Purchase #3 $164.95   7.379%   $177.1217   $177.12   $177.10   $177.10  
  Purchase #4 $81.50   6.741%   $86.9939   $86.99   $87.00   $87.00  
  Purchase #5 $219.48   10.722%   $243.0126   $243.01   $243.00   $243.00  
  Purchase #6 $95.47   4.785%   $100.0382   $100.04   $100.05   $100.00  
  Purchase #7 $203.85   6.773%   $217.6568   $217.66   $217.65   $217.70  
  7 purchase totals = $946.81       $1,015.9333   $1,015.93   $1,015.90   $1,015.90