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 $246.31   8.199%   $266.505   $266.51   $266.50   $266.50  
  Purchase #2 $39.64   5.586%   $41.8543   $41.85   $41.85   $41.90  
  Purchase #3 $230.98   9.791%   $253.5953   $253.60   $253.60   $253.60  
  Purchase #4 $25.74   10.436%   $28.4262   $28.43   $28.45   $28.40  
  Purchase #5 $235.95   6.804%   $252.004   $252.00   $252.00   $252.00  
  Purchase #6 $67.81   9.401%   $74.1848   $74.18   $74.20   $74.20  
  Purchase #7 $249.43   9.641%   $273.4775   $273.48   $273.50   $273.50  
  7 purchase totals = $1,095.86       $1,190.0471   $1,190.05   $1,190.10   $1,190.10