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 $235.51   10.717%   $260.7496   $260.75   $260.75   $260.70  
  Purchase #2 $223.51   3.273%   $230.8255   $230.83   $230.85   $230.80  
  Purchase #3 $207.72   10.199%   $228.9054   $228.91   $228.90   $228.90  
  Purchase #4 $110.45   13.760%   $125.6479   $125.65   $125.65   $125.60  
  Purchase #5 $95.63   11.547%   $106.6724   $106.67   $106.65   $106.70  
  Purchase #6 $73.89   7.276%   $79.2662   $79.27   $79.25   $79.30  
  Purchase #7 $216.65   11.351%   $241.2419   $241.24   $241.25   $241.20  
  7 purchase totals = $1,163.36       $1,273.3089   $1,273.32   $1,273.30   $1,273.20