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 $162.44   7.521%   $174.6571   $174.66   $174.65   $174.70  
  Purchase #2 $63.37   12.435%   $71.2501   $71.25   $71.25   $71.30  
  Purchase #3 $90.64   4.460%   $94.6825   $94.68   $94.70   $94.70  
  Purchase #4 $156.49   7.495%   $168.2189   $168.22   $168.20   $168.20  
  Purchase #5 $236.40   9.171%   $258.0802   $258.08   $258.10   $258.10  
  Purchase #6 $50.58   5.344%   $53.283   $53.28   $53.30   $53.30  
  Purchase #7 $152.60   6.164%   $162.0063   $162.01   $162.00   $162.00  
  7 purchase totals = $912.52       $982.1781   $982.18   $982.20   $982.30