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 $182.49   10.277%   $201.2445   $201.24   $201.25   $201.20  
  Purchase #2 $154.68   6.460%   $164.6723   $164.67   $164.65   $164.70  
  Purchase #3 $225.59   6.313%   $239.8315   $239.83   $239.85   $239.80  
  Purchase #4 $84.33   12.701%   $95.0408   $95.04   $95.05   $95.00  
  Purchase #5 $40.58   10.636%   $44.8961   $44.90   $44.90   $44.90  
  Purchase #6 $209.53   13.747%   $238.3341   $238.33   $238.35   $238.30  
  Purchase #7 $146.28   11.132%   $162.5639   $162.56   $162.55   $162.60  
  7 purchase totals = $1,043.48       $1,146.5832   $1,146.57   $1,146.60   $1,146.50