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 $168.56   3.238%   $174.018   $174.02   $174.00   $174.00  
  Purchase #2 $49.76   4.495%   $51.9967   $52.00   $52.00   $52.00  
  Purchase #3 $52.87   6.204%   $56.1501   $56.15   $56.15   $56.20  
  Purchase #4 $178.42   3.172%   $184.0795   $184.08   $184.10   $184.10  
  Purchase #5 $34.84   7.849%   $37.5746   $37.57   $37.55   $37.60  
  Purchase #6 $208.58   6.825%   $222.8156   $222.82   $222.80   $222.80  
  Purchase #7 $228.86   6.688%   $244.1662   $244.17   $244.15   $244.20  
  7 purchase totals = $921.89       $970.8007   $970.81   $970.75   $970.90