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 $222.32   10.869%   $246.484   $246.48   $246.50   $246.50  
  Purchase #2 $191.67   7.692%   $206.4133   $206.41   $206.40   $206.40  
  Purchase #3 $101.94   13.682%   $115.8874   $115.89   $115.90   $115.90  
  Purchase #4 $23.53   13.869%   $26.7934   $26.79   $26.80   $26.80  
  Purchase #5 $166.65   8.255%   $180.407   $180.41   $180.40   $180.40  
  Purchase #6 $141.39   10.589%   $156.3618   $156.36   $156.35   $156.40  
  Purchase #7 $166.59   5.754%   $176.1756   $176.18   $176.20   $176.20  
  7 purchase totals = $1,014.09       $1,108.5225   $1,108.52   $1,108.55   $1,108.60