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 $163.55   10.253%   $180.3188   $180.32   $180.30   $180.30  
  Purchase #2 $212.44   5.260%   $223.6143   $223.61   $223.60   $223.60  
  Purchase #3 $15.50   6.595%   $16.5222   $16.52   $16.50   $16.50  
  Purchase #4 $60.57   8.438%   $65.6809   $65.68   $65.70   $65.70  
  Purchase #5 $218.76   10.201%   $241.0757   $241.08   $241.10   $241.10  
  Purchase #6 $5.75   11.362%   $6.4033   $6.40   $6.40   $6.40  
  Purchase #7 $127.60   12.230%   $143.2055   $143.21   $143.20   $143.20  
  7 purchase totals = $804.17       $876.8207   $876.82   $876.80   $876.80