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 $227.30   5.284%   $239.3105   $239.31   $239.30   $239.30  
  Purchase #2 $150.44   7.533%   $161.7726   $161.77   $161.75   $161.80  
  Purchase #3 $201.26   11.608%   $224.6223   $224.62   $224.60   $224.60  
  Purchase #4 $91.66   5.426%   $96.6335   $96.63   $96.65   $96.60  
  Purchase #5 $177.81   13.788%   $202.3264   $202.33   $202.35   $202.30  
  Purchase #6 $79.28   11.384%   $88.3052   $88.31   $88.30   $88.30  
  Purchase #7 $223.81   6.870%   $239.1857   $239.19   $239.20   $239.20  
  7 purchase totals = $1,151.56       $1,252.1562   $1,252.16   $1,252.15   $1,252.10