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 $226.66   11.383%   $252.4607   $252.46   $252.45   $252.50  
  Purchase #2 $62.54   9.222%   $68.3074   $68.31   $68.30   $68.30  
  Purchase #3 $191.72   6.623%   $204.4176   $204.42   $204.40   $204.40  
  Purchase #4 $234.77   12.256%   $263.5434   $263.54   $263.55   $263.50  
  Purchase #5 $12.56   10.644%   $13.8969   $13.90   $13.90   $13.90  
  Purchase #6 $17.80   5.534%   $18.7851   $18.79   $18.80   $18.80  
  Purchase #7 $180.51   6.718%   $192.6367   $192.64   $192.65   $192.60  
  7 purchase totals = $926.56       $1,014.0478   $1,014.06   $1,014.05   $1,014.00