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 $127.43   5.381%   $134.287   $134.29   $134.30   $134.30  
  Purchase #2 $185.64   11.331%   $206.6749   $206.67   $206.65   $206.70  
  Purchase #3 $206.62   5.824%   $218.6535   $218.65   $218.65   $218.70  
  Purchase #4 $149.39   10.106%   $164.4874   $164.49   $164.50   $164.50  
  Purchase #5 $231.52   5.305%   $243.8021   $243.80   $243.80   $243.80  
  Purchase #6 $225.40   4.540%   $235.6332   $235.63   $235.65   $235.60  
  Purchase #7 $134.79   4.749%   $141.1912   $141.19   $141.20   $141.20  
  7 purchase totals = $1,260.79       $1,344.7293   $1,344.72   $1,344.75   $1,344.80