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 $203.35   11.234%   $226.1943   $226.19   $226.20   $226.20  
  Purchase #2 $125.50   9.852%   $137.8643   $137.86   $137.85   $137.90  
  Purchase #3 $238.55   3.118%   $245.988   $245.99   $246.00   $246.00  
  Purchase #4 $228.35   4.321%   $238.217   $238.22   $238.20   $238.20  
  Purchase #5 $170.86   5.714%   $180.6229   $180.62   $180.60   $180.60  
  Purchase #6 $17.45   11.533%   $19.4625   $19.46   $19.45   $19.50  
  Purchase #7 $52.71   9.731%   $57.8392   $57.84   $57.85   $57.80  
  7 purchase totals = $1,036.77       $1,106.1882   $1,106.18   $1,106.15   $1,106.20