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 $222.80   6.825%   $238.0061   $238.01   $238.00   $238.00  
  Purchase #2 $226.87   10.420%   $250.5099   $250.51   $250.50   $250.50  
  Purchase #3 $71.88   7.476%   $77.2537   $77.25   $77.25   $77.30  
  Purchase #4 $187.78   12.645%   $211.5248   $211.52   $211.50   $211.50  
  Purchase #5 $178.75   3.120%   $184.327   $184.33   $184.35   $184.30  
  Purchase #6 $156.60   3.387%   $161.904   $161.90   $161.90   $161.90  
  Purchase #7 $134.25   5.421%   $141.5277   $141.53   $141.55   $141.50  
  7 purchase totals = $1,178.93       $1,265.0532   $1,265.05   $1,265.05   $1,265.00