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 $244.82   9.493%   $268.0608   $268.06   $268.05   $268.10  
  Purchase #2 $25.50   8.411%   $27.6448   $27.64   $27.65   $27.60  
  Purchase #3 $57.32   7.748%   $61.7612   $61.76   $61.75   $61.80  
  Purchase #4 $210.84   3.214%   $217.6164   $217.62   $217.60   $217.60  
  Purchase #5 $56.44   4.684%   $59.0836   $59.08   $59.10   $59.10  
  Purchase #6 $162.86   4.870%   $170.7913   $170.79   $170.80   $170.80  
  Purchase #7 $212.50   9.643%   $232.9914   $232.99   $233.00   $233.00  
  7 purchase totals = $970.28       $1,037.9495   $1,037.94   $1,037.95   $1,038.00